Use of composted sewage sludge in growth media for broccoli

High nitrogen addition after the application of sewage sludge compost decreased the bioavailability of heavy metals in soil

Nitrogen (N) fertilizer is highly significant in agricultural production, but long-term N addition causes changes in quality indicators, such as soil organic matter (SOM), thus affecting the absorption and accumulation of organic pollutants. Therefore, paying more attention to organic fertilizers in the development of green agriculture is necessary. However, the accumulation of heavy metals (HMs) contained in organic fertilizers (especially sewage sludge compost (SSC)) in the soil can cause environmental contamination, but how this cumulative reaction changes with the long-term N addition remains unclear. Here the SSC impact on the bioavailability of five typical HMs (cadmium-Cd, chromium-Cr, copper-Cu, lead-Pb and arsenic-As) in the soil-plant system before and after SSC application was demonstrated through a field study in soils with different application rates of 0, 100 and 300 kg N ha^-1yr^-1, respectively. Our results showed that SSC application increased the concentration of most HMs in soil profiles and plant systems (wheat roots and grains), but the accumulation rate of HMs and most bioaccumulation values (BAC-bioaccumulation coefficient and BCF-bioconcentration factor) in plant systems were both lower in high-N addition soil than that in the low-N group. Moreover, speciation distribution results further indicated that SSC application increased the LB (liable available form, including F1-water soluble, F2-ion exchangeable, and F3-bound to carbonates) form of HMs and decreased the PB (potentially available form, including F4-humic acids and F6-fraction bound to organic matter) form of HMs in high-N addition soil, respectively. Those results suggested that HM bioavailability in high-N addition soil was lower than that in low-N addition soil when applied with SSC. Overall, this study found that increasing soil N content can inhibit the bioavailability of HMs when applying SSC, providing suggestions for optimizing the trialability and risk assessment of SSC application.

A critical review on utilization of sewage sludge as environmental functional materials

Sewage sludge (SS) is increasingly used as an environment functional material to reduce or control pollution and improve plant growth because of the large amounts of carbon and essential plant nutrients in it. To achieve the best application results, it is essential to comprehensively review recent progress in SS utilization. This review aims to fill the gaps in knowledge by describing the properties of SS, and its usage as adsorbents, catalysts and fertilizers, and certain application mechanisms. Although SS generates several benefits for the environment and humans, many challenges still exist to limit the application, including the risks posed by potentially toxic substances (e.g., heavy metals) in SS. Therefore, future research directions are discussed and how to make SS applications more feasible in terms of technology and economy.

Feasibility of Biochar Derived from Sewage Sludge to Promote Sustainable Agriculture and Mitigate GHG Emissions-A Review

Sewage sludge (SS) has been connected to a variety of global environmental problems. Assessing the risk of various disposal techniques can be quite useful in recommending appropriate management. The preparation of sewage sludge biochar (SSB) and its impacts on soil characteristics, plant health, nutrient leaching, and greenhouse gas emissions (GHGs) are critically reviewed in this study. Comparing the features of SSB obtained at various pyrolysis temperatures revealed changes in its elemental content. Lower hydrogen/carbon ratios in SSB generated at higher pyrolysis temperatures point to the existence of more aromatic carbon molecules. Additionally, the preparation of SSB has an increased ash content, a lower yield, and a higher surface area as a result of the rise in pyrolysis temperature. The worldwide potential of SS output and CO₂-equivalent emissions in 2050 were predicted as factors of global population and common disposal management in order to create a futuristic strategy and cope with the quantity of abundant global SS. According to estimations, the worldwide SS output and associated CO₂-eq emissions were around 115 million tons dry solid (Mt DS) and 14,139 teragrams (Tg), respectively, in 2020. This quantity will rise to about 138 Mt DS sewage sludge and 16985 Tg CO₂-eq emissions in 2050, a 20% increase. In this regard, developing and populous countries may support economic growth by utilizing low-cost methods for producing biochar and employing it in local agriculture. To completely comprehend the benefits and drawbacks of SSB as a soil supplement, further study on long-term field applications of SSB is required.

Treatment processes to eliminate potential environmental hazards and restore agronomic value of sewage sludge: A review

Land application of sewage sludge is increasingly used as an alternative to landfilling and incineration owing to a considerable content of carbon and essential plant nutrients in sewage sludge. However, the presence of chemical and biological contaminants in sewage sludge poses potential dangers; therefore, sewage sludge must be suitably treated before being applied to soils. The most common methods include anaerobic digestion, aerobic composting, lime stabilization, incineration, and pyrolysis. These methods aim at stabilizing sewage sludge, to eliminate its potential environmental pollution and restore its agronomic value. To achieve best results on land, a comprehensive understanding of the transformation of organic matter, nutrients, and contaminants during these sewage-sludge treatments is essential; however, this information is still lacking. This review aims to fill this knowledge gap by presenting various approaches to treat sewage sludge, transformation processes of some major nutrients and pollutants during treatment, and potential impacts on soils. Despite these treatments, overtime there are still some potential risks of land application of treated sewage sludge. Potentially toxic substances remain the main concern regarding the reuse of treated sewage sludge on land. Therefore, further treatment may be applied, and long-term field studies are warranted, to prevent possible adverse effects of treated sewage sludge on the ecosystem and human health and enable its land application.

Machine Learning Approach to Predict Quality Parameters for Bacterial Consortium-Treated Hospital Wastewater and Phytotoxicity Assessment on Radish, Cauliflower, Hot Pepper, Rice and Wheat Crops

Raw hospital wastewater is a source of excessive heavy metals and pharmaceutical pollutants. In water-stressed countries such as Pakistan, the practice of unsafe reuse by local farmers for crop irrigation is of major concern. In our previous work, we developed a low-cost bacterial consortium wastewater treatment method. Here, in a two-part study, we first aimed to find what physico-chemical parameters were the most important for differentiating consortium-treated and untreated wastewater for its safe reuse. This was achieved using a Kruskal–Wallis test on a suite of physico-chemical measurements to find those parameters which were differentially abundant between consortium-treated and untreated wastewater. The differentially abundant parameters were then input to a Random Forest classifier. The classifier showed that ‘turbidity’ was the most influential parameter for predicting biotreatment. In the second part of our study, we wanted to know if the consortium-treated wastewater was safe for crop irrigation. We therefore carried out a plant growth experiment using a range of popular crop plants in Pakistan (Radish, Cauliflower, Hot pepper, Rice and Wheat), which were grown using irrigation from consortium-treated and untreated hospital wastewater at a range of dilutions (turbidity levels) and performed a phytotoxicity assessment. Our results showed an increasing trend in germination indices and a decreasing one in phytotoxicity indices in plants after irrigation with consortium-treated hospital wastewater (at each dilution/turbidity measure). The comparative study of growth between plants showed the following trend: Cauliflower > Radish > Wheat > Rice > Hot pepper. Cauliflower was the most adaptive plant (PI: −0.28, −0.13, −0.16, −0.06) for the treated hospital wastewater, while hot pepper was susceptible for reuse; hence, we conclude that bacterial consortium-treated hospital wastewater is safe for reuse for the irrigation of cauliflower, radish, wheat and rice. We further conclude that turbidity is the most influential parameter for predicting bio-treatment efficiency prior to water reuse. This method, therefore, could represent a low-cost, low-tech and safe means for farmers to grow crops in water stressed areas.

Potential of developing podzolic soil-based potting media from wood ash, paper sludge and biochar

BACKGROUND AND OBJECTIVES

Organic waste management in environmentally sustainable way is important not only to reduce the negative impacts on ecosystems but also valorizing the waste resources. Herein we evaluated the potential of wood ash (WA) and paper sludge (PS) wastes from a pulp and paper mill as potting media and their effects on the physicochemical properties of podzolic soil.

METHODS

WA, PS and biochar (BC) was mixed in different combinations with a sandy loam podzolic soil. Potting media treatments included: T1-soil (negative control); T2-Promix^TM (positive control); T3-50%soil+50%WA; T4-75%soil+25%WA; T5-50%soil+50%PS; T6-75%soil+25%PS; T7-75%soil+25%BC; T8-25%soil+50%WA+25%BC; T9-50%soil+25%WA+25%BC; T10-25%soil+50%PS+25%BC; T11-50%soil+25%PS+25%BC, T12- 25%soil+25%WA+25%PS+25%BC and replicated three times.

RESULTS

Potting media treatments expressed significant (p < 0.00) effects on pH, bulk density, total porosity, field capacity, plant available water (PAW) and water retention curves. Potting media amended with WA showed high pH range (8-12) while PS amendments exhibited pH in range where most plant nutrients are available (6.5-7.5). Results depicted significantly lower bulk density, and increased total porosity and water holding capacity of potting media amended with WA and PS. BC addition further enhanced the water retention properties compared to combinations without BC. T6, T10 and T11 produced higher amounts of PAW with desired pH compared to T1 and T2.

CONCLUSION

WA, PS and BC showed high potential for developing podzolic soil-based potting media, but their effects on plant growth and elemental uptake need to be investigated.

Evaluation of Land Potential for Use of Biosolids in the Coastal Mediterranean Karst Region

The aim of this study was to evaluate the potential of agricultural land in the coastal Adriatic Karst region (Šibenik region, Croatia) for biosolids application by integrating spatial data from different sources: digital maps and remote sensing, parcel identification system, GIS field observations and measurements focusing on specific land and soil properties. Due to the rapid development of the wastewater treatment industry, excessive accumulation of sewage sludge (SS) in wastewater treatment plants is a growing problem worldwide. Management options for land application of biosolids require a comprehensive characterization of both SS and SS-amended soils. The assessment of agricultural land in the study area for SS disposal was based on EU and national legislation. The evaluation revealed that agricultural land in the study area accounts for only 10% of the total area (25,736 ha), but only a quarter of the existing land (6065 ha) is suitable for biosolids application. Furthermore, the data indicate that the sewage sludge can be safely applied to the soil in terms of soil metals according to the Croatian legislation. The short-term potential of the soil to sustain this ecosystem service, namely soil improvement with biosolids, should be used to determine the inherent long-term potential based on resistance to soil degradation and resilience. However, caution is needed and the long-term effects should be investigated before biosolids are continuously used for soil application.

Influence of tomato waste compost ratios on plant growth and fruit quality of cucumber and summer squash

Peat-moss (Sphagnum spp.), is currently an expensive material and a nonrenewable resource with variable properties. Therefore, its use should be gradually reduced. Hence, there are numerous attempts aiming to reduce the use of peat-moss as a bulk substrate and to search for high-quality, locally available and low-cost alternatives to peat-moss. Therefore, the main objective of this research is to investigate the effect of partial replacing of peat-moss with tomato waste compost (TWC) on plant growth, productivity, fruit quality, and morphological features of two types of economic cucurbits species under greenhouse conditions. The plants were planted into pots containing different proportions of TWC (0%, 5%, 10%, 15%, 20% and 30%) with peat-moss, sand and clay as growing substrates. The results indicated that the plant height and the leaves number of both plants were significantly influenced by different substrate treatments. TWC ratios of 15% and 20% increased the amount of cucumber and summer squash fruit yield more than the commercial peat media but they had insignificant differences. Also, they were significantly improved fruit quality characteristics, particularly total soluble solid (TSS) and titratable acidity (TA) of crop fruits more than commercial peat-moss treatment.Implications: Because of the high price of peat-moss and that it is a non-renewable material, farmers resorted to using other alternatives, including green residue compost. Thus, the aim of this work is to reduce the use of peat-moss by replacing it with the use of lokw percentages of TWC. When tomato plant residues return to the soil by converting them into compost, this is a valuable agricultural practice to improve soil fertility and increase the organic matter of the soil as well as increase the source of nitrogen (N) that supports the growth of beneficial microorganisms.

Effect of sewage sludge derived compost or biochar amendment on the phytoaccumulation of potentially toxic elements and radionuclides by Chinese cabbage

This study set out to evaluate the effect of using sewage sludge-derived compost (SSC) or biochar (SSB) as a soil amendment on the phytoaccumulation of potentially toxic elements, PTE (Cd, Cr, Cu, Ni, Pb, Zn) and natural radionuclides (²³⁸U and ²³²Th) by Chinese cabbage (Brassica rapa L. subsp. pekinensis (Lour.) Hanelt) in terra rossa and rendzina soils, which are the two common soil types in Croatia. The experiment consisted of a greenhouse pot trial using a three-factor design where soil type, sludge post-stabilisation procedure and amendment rate (12 and 120 mgP/L) were the main factors. At harvest, the concentrations of analytes in the substrate, leaves and roots were measured, from which the edible tissue uptake (ETU) and concentration ratios (CR) were determined. Also, the average daily dose (ADD) and hazard quotient (HQ) were determined to assess the health risk, as well as soil contamination factor (CF). The results showed that neither adding SSC nor SSB affected the soil loading at the rates applied, suggesting a low risk of soil contamination (CF ≤ 1). The ETU of Cd, Cu, and Zn were 0.0061, 1.23, and 0.91 mg/plant from compost-amended soil and 0.0046, 0.78 and 0.65 mg/plant for biochar-amended soil, respectively. This difference suggests that their ETU was higher in compost-amended soils than in soils treated with biochar. The CR data indicate that the bioavailability of Cu (CR of 5.30) is highest at an amendment rate of 12 mgP/L, while for Zn (CR of 0.69), the highest bioaccumulation was observed with an amendment rate of 120 mgP/L. Translocation of Cr, Ni, Pb and ²³⁸U to the leaves was limited. Overall, the HQ (<1) for Cd, Cu and Zn in the edible parts confirmed that consuming Chinese cabbage does not threaten human health. Similarly, the daily intake of ²³²Th remained below the limit (3 μg) set by ICRP, suggesting no radiological risk. Finally, although the amendment rate, which was 10-times the amount stipulated in Croatian regulation and the CR ranged from 0.007 to 5.30, the precautionary principle is advised, and the long-term impact of sewage sludge derived compost or biochar on different plant groups (incl. root vegetables) at the field-scale is recommended.

The use of spent coffee grounds in growing media for the production of Brassica seedlings in nurseries

Large quantities of spent coffee grounds (SCG) are generated the last decades, and their recycling is of research interest challenge. In the present study, SCG was tested to substitute peat (P) in substrate mixtures for the production of Brassica seedlings. Seeds of cauliflower, broccoli, and cabbage were placed in substrate mixtures containing 0-2.5-5-10% SCG. The mixture of SCG with peat affected several physicochemical characteristics of the growing media, providing also considerable amount of mineral elements for the seedling growth needs. Seed emergence was stimulated in 2.5-5% of SCG for cauliflower and at 2.5% of SCG for cabbage, while 10% of SCG decreased the percentage and increased the mean emergence time of the examined species. Plant biomass and leaf number were increased at 2.5% SCG for broccoli and cabbage but maintained at cauliflower when compared with control. The SCG at 10% decreased stomatal conductance of broccoli and cabbage (including 2.5-5% SCG in cauliflower) while chlorophyll content was increased at 10% of SCG media. The incorporation of SCG impacted the mineral content accumulated in plants with increases in nitrogen, potassium, and phosphorus and decreases in magnesium and iron content. Total phenolics and antioxidant activity (DPPH, FRAP) decreased at ≥ 5% SCG at cauliflower and cabbage or unchanged for broccoli when compared with the control. The cabbage seedlings grown in 10% SCG media subjected to stress with increases in the production of hydrogen peroxides and lipid peroxidation, and reflected changes in the antioxidant enzymatic metabolism (catalase, superoxide dismutase). The present study demonstrates that SCG (up to 5%) can be used for seed germination biostimulants and/or partially substitute the peat for Brassica seedling production.

Increasing plant phosphorus availability in thermally treated sewage sludge by post-process oxidation and particle size management

Thermal conversion of phosphorus (P)-rich waste materials such as sewage sludge offers several advantages: generation of bioenergy, concentration of plant nutrients and the destruction of organic pollutants. Different thermal processes modify the feedstock's chemical and physical structure in differing ways, which also affects P speciation and plant availability in the residual ashes or carbonization products. This study assessed to which extent the P plant availability of ashes and chars produced from one batch of sewage sludge by incineration, pyrolysis or gasification was affected by particle size management and post-process oxidation. Overall, a smaller particle size of the materials as well as post-process oxidation of non-oxidized materials increased the amount of plant-available P in the soil. In a pot experiment, all the materials increased plant biomass compared with the untreated control, but the pyrolysis chars had a substantially greater fertiliser value than the gasification ashes, while the two tested incineration ashes differed in their P fertilizing effect. P availability in non-oxidized materials was partly related to lower process temperatures and lower levels of crystallinity. However, downstream oxidation simultaneously increased crystallinity and P availability in a pyrolysis char and gasification ashes, resulting in an increase in plant P uptake of up to 60%. Results indicate that the oxidation of poorly soluble Fe-phosphates may contribute to the positive effect on P availability. The results suggest that changes to the design and settings of the thermal conversion processes of sewage sludge offer considerable potential for improving P availability in the residual material.

Recycling of Organic Wastes through Composting: Process Performance and Compost Application in Agriculture

Composting has become a preferable option to treat organic wastes to obtain a final stable sanitized product that can be used as an organic amendment. From home composting to big municipal waste treatment plants, composting is one of the few technologies that can be practically implemented at any scale. This review explores some of the essential issues in the field of composting/compost research: on one hand, the main parameters related to composting performance are compiled, with especial emphasis on the maturity and stability of compost; on the other hand, the main rules of applying compost on crops and other applications are explored in detail, including all the effects that compost can have on agricultural land. Especial attention is paid to aspects such as the improvement of the fertility of soils once compost is applied, the suppressor effect of compost and some negative experiences of massive compost application.

Application of stabilized sludge to extensive green roofs in Shanghai: Feasibility and nitrogen leaching control

Extensive green roofs, in which commercial compost is usually used as organic component, have great potential to mitigate some environmental problems caused by urbanization, but carry risks of nutrients leaching into downstream aquatic. Stabilized sludge (SS) from wastewater treatment plants could be potentially used as nutrient component for green roof, but the effects on effluent quality are uncertain. To investigate the problem, a pilot experiment was conducted under field conditions, the effluent quality of green roof using SS was compared with green roofs using peat soil and controlled release fertilizer. In the field experiment, the nutrient concentrations in effluent of the green roof using SS (TN, NO₃^--N, NH₄⁺-N and TP were 3.27 mg/L, 1.75 mg/L, 1.14 mg/L and 0.34 mg/L, respectively) were not significantly different from the green roofs using peat soil and controlled release fertilizer, and the chemical oxygen demand level (92 mg/L) was lower than the roofs using compost or commercial substrate. To reduce the environmental risks caused by the application of SS to green roofs, a laboratory test was carried out to analyze the effects of biochar and dual-substrate structure on nitrogen leaching. The results showed that both biochar and dual-substrate reduced nitrogen leaching, and nitrogen leaching from green roofs using SS was a combined effect of organic nitrogen mineralization during dry period and biological processes during wet period. A high temperature and low humidity environment which is common in green roofs reduced nitrate accumulation during dry period, and nitrate was transformed to other substances in gaseous form by denitrification, which tended to occur in long duration, low intensity rainfall events. The results suggest that the application of stabilized sludge to green roofs is feasible in area where average rain intensity is not high, preferably combined with amendment of biochar and a dual-substrate structure.

Printed Paper Waste as an Alternative Growing Medium Component to Produce Brassica Seedlings under Nursery Conditions

Significant quantities of paper waste (PW) have been accumulated in recent years and the reuse/recycling of PW is required due to environmental concerns. In the present study, printed PW was used as a peat (P) substitute in growing medium for the Brassica seedlings production, considering recycling, sustainable agriculture, and partly peat replacement. Seeds of cauliflower, broccoli, and cabbage were seeded in growing media made of 0–10–30–50% PW. The addition of PW improved the growing media pH and mineral content, reduced the media aeration, and affected seed emergence. The PW decreased plant growth and the effects were more pronounced at 50% PW. The PW ≥ 30% decreased stomatal conductance, while chlorophyll fluorescence and content of chlorophylls decreased with high PW ratio, negatively affecting the plant physiology. The PW decreased plant sodium and iron and increased potassium, calcium, magnesium, and copper content. The PW increased antioxidant activity to a certain degree for cauliflower and cabbage and resulted in no change for broccoli, while polyphenols increased in cabbage seedlings. The addition of PW did not cause cellular damage as both lipid peroxidation and hydrogen peroxide production remained at low levels, maintaining low levels on the antioxidant enzymes (catalase, superoxide dismutase, peroxidase) metabolism. The present study shows that low PW content can partially replace peat for Brassica seedling production under a sustainable agriculture and environmentally friendly scheme.

Deployment of olive-stone waste as a substitute growing medium component for Brassica seedling production in nurseries

In the Mediterranean region, olive-stone waste (OSW) is accumulated and considered of environmental and human health constraints. In this study, OSW was used for peat (P) replacement in growing media for Brassica seedling production. Cauliflower, broccoli, and cabbage were seeded in growing media consisted of 0-20-40-60% OSW. The mixture of OSW with peat increased growing media bulk density and reduced the total pore space and available water and air at root system. A Considerable amount of minerals were provided into the growing media with the OSW, while their availability was increased with the raised pH values. Seed emergence percentage decreased with high ratio of OSW which also increased mean emergence time. The addition of OSW decreased plant height, leaf number, and fresh weight in all three examined species. The OSW decreased stomatal conductance (in cauliflower and cabbage) and chlorophylls content (including broccoli). The insertion of OSW affected the mineral accumulation in plants with decreases in nitrogen and sodium content and increases in potassium and calcium. OSW increased to some extent for cauliflower and broccoli or unchanged for cabbage polyphenolic content and antioxidant activity (ABTS, FRAP). Cellular damage was caused by the addition of OSW by increasing the lipid peroxidation and the production of hydrogen peroxide, and as a consequence, the plant antioxidative (catalase, superoxide dismutase) enzyme metabolism increased. The current study demonstrates that up to 20% of OSW can substitute peat for cauliflower, broccoli, and cabbage seedling production while cabbage was performed better under the increased OSW-caused stress.

Evaluation of anaerobic digestates from sewage sludge as a potential solution for improvement of soil fertility

Sewage sludge production in European countries has widely raised in the last decade and its fate is currently landfilling, incinerators, composting or land application. To explore its agronomic potential, the main target of this work is to understand the effects of anaerobic digestates from sewage sludge (SSAD). To this aim, four different SSADs (two liquids and two dewatered) were characterized. On the liquid ones, Germination Index was evaluated through a plate bioassay with Lepidium sativum L. seeds; low concentrations of SSAD (2.5%) improved GI in one case, while at higher concentrations phytotoxic effects occurred in both. Then, pot experiments were set in climate chamber with Cucumis sativus L. grown for 30 days on two different substrates: a sandy, alkaline and poor soil, and peat substrate. All SSADs and a mineral fertilizer were used at three increasing dosages: 85, 170, 255 kg of nitrogen per hectare (kg N/ha). Results in terms of germination, dry biomass, chlorophyll content, net photosynthesis, stomatal conductance, CO₂ concentration in substomatal cavity and root development were compared to a not treated control. All treatments gave results significantly higher or similar to control on all the parameters evaluated. Moreover, the intermediate nitrogen dosage (170 kg N/ha) generally showed the highest results compared to other dosages, especially for dewatered SSADs. All these results were much more evident for cucumber plants grown on an the alkaline, sandy and poor soil than on peat substrate, such demonstrating that SSADs have a fertilizing effect for plants growing on this kind of soil.

Adding Phosphate Fertilizer and Apple Waste to Pig Manure during Composting Mitigates Nitrogen Gas Emissions and Improves Compost Quality

Calcium superphosphate and apple ( Mill.) waste can be used for controlling N loss and improving compost quality during composting, whereas integrated addition of the two additives on composting process remains unexplored. Therefore, this study was conducted to investigate the effects of combined use of calcium superphosphate and apple waste on NH and NO emissions and compost quality during pig manure and wheat ( L.) straw composting. Mixtures of pig manure and wheat straw were combined with 6% phosphate fertilizer (PF), 15% apple waste (AW), 3% phosphate fertilizer + 7.5% apple waste (PA1), or 1.8% phosphate fertilizer + 10.5% apple waste (PA2) based on dry weight of the initial mixtures; a treatment with no additives served as a control (CK). The PF treatment took 3 d longer to reach thermophilic phase than the CK, PA1, and PA2 treatments. The treatments of PF and PA1 reduced NH and NO emissions by 67 and 45%, respectively. Moreover, N loss in PF and PA1 treatments (31.8 and 30.1%, respectively) was significantly less than in the CK. A pot experiment showed that application of the compost with PA1 treatment could increase plant height and dried biomass of Chinese pakchoi ( L. ssp.). We recommend adding 3% phosphate fertilizer and 7.5% apple waste to pig manure during composting.

Enhanced soil fertility, plant growth promotion and microbial enzymatic activities of vermicomposted fly ash

It is reported that coal consumption in the Asia-Pacific region is going to increase to about 87.2 percent by 2035. Management of coal combustion residues (CCRs) generated by industries is a major bottleneck towards handling the repercussions of coal usage. The present study investigates a management technique for these potentially hazardous wastes by means of vermicomposting. In the present investigation, studies were made on the effects of various concentrations of vermicomposted fly ash (VCF) added to agricultural soil, on the growth and yield of tomato (Lycopersicon esculentum Mill.) and brinjal (Solanum melongena L.) plants. The toxicity of trace elements in VCF were estimated using coefficient of pollution and potential ecological risk index, which revealed no apparent risks to the environment. A gradual increase in VCF concentrations in the agricultural soil improved the physico-chemical properties, enzymatic activities, microbial biomass, carbon and microbial population upto 90 days after sowing of seeds. The VCF amendments significantly (p < 0.05) improved the soil quality (2.86% nitrogen and 1.05% Phosphorous) and germination percentage (82.22%) of seeds in L. esculentum and also in S. melongena. The results of this study reveal that, CCRs can be effectively managed in agriculture specially in developing economies.

The effect of stabilization on the utilization of municipal sewage sludge as a soil amendment

This study assesses the potential use of different types of stabilized sewage sludge as a soil amendment by considering their physicochemical characteristics, nutritional status, and their trace metal and radionuclide content. The concentrations of trace metals and radionuclides were determined using ICP-OES and gamma-ray spectrometry, respectively. For determining nutritional status and chemical characterization, this study followed standard ISO-recommended procedures. Data analysis revealed that anaerobic sludge contains higher concentrations of Cr, Hg, and Ni compared to aerobic and non-biologically stabilized sludge. A similar observation was observed in the case of ²²⁶Ra, ²¹⁰Pb, ²²⁸Ra, and ²²⁸Th. Furthermore, the high levels of P and N in aerobic sludge suggest that biologically stabilized sludge has the potential to be a good fertilizer. In addition, the study finds strong evidence that nutrients are involved in the adsorption of metals and radionuclides onto sludge biomass. Overall, eight of the nine studied sludge samples are safe for agricultural use since the concentrations of trace metals fall well below the limits set by Croatian legislation (NN 38/08). In addition, the levels of radionuclides do not pose a radiological risk. This means that soil conditioning with sewage sludge remains a viable strategy for nutrient recovery from municipal waste, although long-term impact assessments of repeated applications are necessary.

Response of Weeping Lantana (Lantana montevidensis) to Compost-Based Growing Media and Electrical Conductivity Level in Soilless Culture: First Evidence

The most common substrate for potted ornamental plants is prepared with Sphagnum peat; however, the cost and declining availability of high-quality peat, due to environmental constraints, make it necessary to investigate for alternative organic materials. The present study aimed to determine the effects of partial compost replacement with peat and the optimum electrical conductivity (EC) level of the nutrient solution in potted weeping lantana [L. montevidensis (Spreng.) Briq.] under a recirculating soilless system. Three compost-based substrates were prepared by mixing peat (Pe) with sewage sludge-based compost (Co.) at a rate of 0% (Pe90Co0Pu10, control), 30% (Pe60Co30Pu10), or 60% (Pe30Co60Pu10), respectively. The soilless recirculated closed system was equipped with two different EC levels (high and low) of nutrient solution. Growing media main characteristics and plant bio-morphometric parameters were evaluated. Our first evidence clearly demonstrates that the replacement of peat with compost at doses of 30% and 60% gave the poorest results for plant diameter, shoots, leaves, flowers, and fresh and dry mass, probably indicating that the physical characteristics of the compost based substrates may be the major factor governing plant growth rate. Compost media pH and EC values, too, showed negative effects on plant growth. Considering the effect of EC level, all morphological traits were significantly improved by high EC compared to low EC in weeping lantana. Thus, based on first evidence, further research is needed on organic materials for the establishment of ecological substrates with optimal physicochemical characteristics for the growth of weeping lantana.

Effects of municipal solid waste- and sewage sludge-compost-based growing media on the yield and heavy metal content of four lettuce cultivars

Compost has been recently suggested as an alternative to peat for the preparation of growing substrates in soilless cultivation systems. However, some physico-chemical properties of compost may reduce plant performance and endanger the quality of productions, in particular for possible heavy metal accumulation in edible parts. This study aims at evaluating the suitability of a municipal solid waste compost (MSWC) and a sewage sludge compost (SSC) as components of growing media for the soilless cultivation of lettuce (Lactuca sativa L.). Heavy metal content of SSC complied with legislation limits but, in MSWC, it exceeded (Cu, Pb) or was very close (Cd, Zn) to safe limits. A greenhouse experiment was carried out by cultivating four lettuce cultivars ("Maximus," "Murai," "Patagonia," and "Aleppo") in pots containing a mixture of MSWC and perlite (MSWC + P), SSC and perlite (SSC + P), or peat and perlite (peat + P), the latter used as control. Plant biometric parameters measured after 72 days of growth revealed that the yield of plants cultivated on SSC + P was similar to control plants, independently of the cultivar. Conversely, MSWC + P suppressed in general the biomass production, especially for Murai and Patagonia cultivars. Compared to peat + P, both compost-based substrates reduced the leaf accumulation of heavy metals, with a major effect in Maximus plants. The levels of Cd and Pb in the edible part were always below the safe limits imposed by European regulation. Therefore, risks of heavy metal intake in food chain associated with the replacement of peat with compost in the growing media are negligible, even when a compost with a significant amount of heavy metals is used. Besides compost quality monitoring, also an appropriate varietal choice is crucial to obtain good yields and safe products.

Agroindustrial composts to reduce the use of peat and fungicides in the cultivation of muskmelon seedlings

BACKGROUND

Environmental concerns about peat extraction in wetland ecosystems have increased. Therefore, there is an international effort to evaluate alternative organic substrates for the partial substitution of peat. The aim of this work was to use different composts (C1-C10) obtained from the fruit and vegetable processing industry (pepper, carrot, broccoli, orange, artichoke residues, sewage sludge (citric and pepper) and vineyard pruning wastes) to produce added-value composts as growing media with suppressive effect against Fusarium oxysporum f.sp. melonis (FOM) in muskmelon.

RESULTS

Composts showed values of water-soluble carbon fractions and dehydrogenase activity that allowed them to be considered mature and stabilized. All compost treatments produced significantly (F = 7.382; P < 0.05) higher fresh shoot weight than peat, treatment T-C2 showing the highest values. Treatments T-C5, T-C7 and T-C8 showed percentages of disease incidence that were significantly (F = 16.052; P < 0.05) the lowest, relative to peat, followed by T-C6, T-C10, T-C1 and T-C9 with values below 50%.

CONCLUSION

Composts produced are suitable components of mixed compost-peat growing media, providing a 50% substitution of peat. Furthermore, some of these composts also showed an added value as a suppressive organic medium against Fusarium wilt in muskmelon seedling, a fact probably related to high pH and pepper wastes and high content of pruning waste as initial raw materials. © 2016 Society of Chemical Industry.

Agroindustrial compost as a peat alternative in the horticultural industry of Ecuador

This work was conducted in order to investigate the possibility of using different agroindustrial composts in the production of horticultural seedlings, thereby replacing part of the peat in the growing media. Three vegetable species differing in salt sensitivity - tomato (Solanum lycopersicum L. var. Malpica) (the least sensitive), courgette (Cucurbita pepo L. var. Mastil F1) (moderately sensitive) and pepper (Capsicum annuum L. var. Largo de Reus Pairal) (the most sensitive) - were grown in nine media containing three composts, prepared by co-composting vegetable waste (flower, broccoli or tomato waste) with laying hen manure and sawdust, as well as peat in various ratios. The proportions of the three composts in the mixtures elaborated with peat were 25%, 50% and 75% (v/v). A substrate of 100% peat was used as control. The experiment was arranged in a completely-randomised design, with two replicates per treatment, under greenhouse conditions. Prior to sowing, some physical, physico-chemical and chemical properties of the growing media were determined and the seed germination and fresh and dry weights of the aerial parts and roots of the seedlings were also measured, as well as the mineral composition of the aerial parts of the plants. In most cases, the addition of compost to the growing media produced an increase in the pH, salt content and macronutrient concentrations, in comparison to peat, whereas the physical properties of the compost based-substrates had values very similar to those of an ideal substrate. Also, multivariate analysis showed that the media prepared with flower waste compost, at all concentrations, and the medium with tomato waste compost at 25% were the most suitable substrates for the three plant species tested.

Response of wine grape growth, development and the transfer of copper, lead, and cadmium in soil-fruit system to sludge compost amendment

Sludge is an organic waste after domestic sewage being treated and contains phytonutrients and organic matter. In this study, recycling of sludge compost (SC) and its compound fertilizer (SCF) to wine grape resulted in improvement in vegetative growth, reproductive development of wine grape, and potential wine quality of grape fruit. The amounts of Cu, Pb, and Cd in grape fruit were significantly higher in response to sludge amendment than in the control, but were all below the permissible limits for agricultural product. The contents of Cu and Pb in sludge-amended soil decreased with increasing soil depth, but Cd content increased with soil depth. Ongoing monitoring of on mobility of Cd downward is proposed with sludge recycling to wine grape soil.

Posidonia oceanica (L.) based compost as substrate for potted basil production

BACKGROUND

Peat is the main component of growing media but is also a non-renewable resource; therefore European policy strongly encourages the use of peat alternatives such as compost. Posidonia is a Mediterranean seagrass that produces very conspicuous onshore deposits that can be composted. In this study, a commercial green compost and a Posidonia residue-based compost were tested in order to assess their potential use as substitutes or complements to peat.

RESULTS

All macro and micro-element concentrations of the substrates were positively and significantly related to the percentage of composts in the growing media. Plant grown on peat showed higher content of P, Ca, K, Na, Cu, Mn, Zn and Fe, and a slightly higher biomass production in comparison to compost-based growing media. In contrast, plants grown on compost-based substrates showed lower uptake of Cd and Cr than peat.

CONCLUSION

The results indicate that both composts can be used as a complement to the peat for substrate preparation, especially at a rate of 30%. The Posidonia-based compost showed better productive results in comparison to the green one. Basil grown on the two compost-based media showed reduced absorption level of potentially toxic metals in comparison to peat.

Elevating concentrations of capsaicin and dihydrocapsaicin in hot peppers using recycled waste

Five Capsicum accessions (PI 435916 and PI 438614 from Capsicum chinense; PI 370004 and Grif 9354 from C. baccatum and PI 438649 from C. annuum) were selected from the U.S. Department of Agriculture-Agricultural Research Service Capsicum germplasm collection to study the impact of four soil management practices: yard waste (YW), sewage sludge (SS), chicken manure (CM) and no-mulch (NM) bare soil on fruit concentrations of capsaicin and dihydrocapsaicin, yield, plant size and mature fruit characteristics (fruit weight, length, width, and wall-thickness) of plants grown under these practices. Regardless of soil treatments, PI 438614 and PI 435916 contained the greatest concentrations of total capsaicinoids (capsaicin and dihydrocapsaicin). Fruits of plants grown in soil mixed with SS contained the greatest concentrations of total capsaicinoids. Fruits of plants grown in SS or CM contained the greatest fruit weight. PI 438649 produced the greatest fruit weight, length and wall-thickness. The total marketable yield expressed as weight of fruit plants was significantly higher in soils mixed with SS and CM compared to those mixed with YW and NM soils.

Improvement of salinity in sewage sludge compost prior to its utilization as nursery substrate

Soluble salts are enriched in sewage sludge compost because of their inherent derivation. Accordingly, the content of soluble salt in sludge compost is usually much higher than most seedlings can tolerate. To determine whether sludge compost is suitable for use as a nursery substrate, some experiments were conducted. Reduction of the electrical conductivity (EC) value could improve seed germination in saturated extract from sludge compost. In addition, water elution and mixing dilution with raw soil were all shown to be able to alleviate saline inhibition on seed germination and seedling growth, including stem diameter, seedling height, and above-ground weight. Overall, salinity is a crucial problem when sewage sludge compost is reused as a nursery substrate, and some effective and convenient approaches to reduce salt should be served prior to its reuse.

IMPLICATIONS

Sewage sludge after being composted is usually reused as organic fertilizer or plant substrate. However, salt is the main problem during its reclamation. What is the highest salt level the seedling can tolerate? Which types of salts are effective in salinity of sludge-amended substrate? Meanwhile, can the salinity be reduced through water elution or soil mixing dilution? This paper is the first to investigate the salinity and its reduction of sewage sludge compost prior to its use in the development of nursery substrate.

Nutrient and enzymatic changes of hydrolysed tannery solid waste treated with epigeic earthworm Eudrilus eugeniae and phytotoxicity assessment on selected commercial crops

Animal fleshing (ANFL) is the predominant proteinaceous solid waste generated during processing of leather and it is confronting disposal problems. The aim of this study was to assess the potential of epigeic earthworm Eudrilus eugeniae to utilize and transform the fermented ANFL in the solid state (SSF) and submerged state (SmF) into a value added product along a low residence period (25 days). A total of six treatment units containing different waste mixture compositions were established. Fifty healthy and non-clitellated earthworms were introduced in three different treatment containers: control, SSF, and SmF (+worm). Another set of treatment mixtures (control, SSF, SmF) was established without earthworms (-worm) to compare the results. The products were characterized for physico-chemical, enzymatic analysis and seedling growth parameters to compare the differences in the process with and without earthworms. The changes observed in the analytical parameters were in the following order: SSF > SmF > control mixtures (p < 0.05). The vermicompost showed a significant reduction in heavy metals, total organic carbon and an increase in total Kjeldhal nitrogen as compared to the product untreated by earthworms. The maximum enzymatic activities were observed after 21 days of vermicomposting. The relative seed germination of vermicompost extracts were in the order of tomato (Lycopersicon esculentum) > green gram (Vigna radiata) > cucumber (Cucumis sativus) > bottle gourd (Lagenaria siceraria (Mol.) Standl.) and showed no phytotoxicity effects. The results indicated that the combination of both ANFL hydrolysis through fermentation and vermicomposting is a good alternative to the management of this kind of waste.

Composted green waste as a substitute for peat in growth media: effects on growth and nutrition of Calathea insignis

Peat mined from endangered wetland ecosystems is generally used as a component in soilless potting media in horticulture but is a costly and non-renewable natural resource. The objective of this work was to study the feasibility of replacing peat with different percentages (0, 10, 30, 50, 70, 90, and 100%) of composted green waste (CGW) as growth media for the production of the ornamental plant Calathea insignis. Compared with 100% peat media, media containing CGW had improved physical and chemical characteristics to achieve the acceptable ranges. Moreover, CGW addition had increased the stability (i.e., reduced the decomposition rates) of growth media mixtures, as indicated by comparison of particle-size distribution at the start and end of a 7-month greenhouse experiment. Addition of CGW also supported increased plant growth (biomass production, root morphology, nutrient contents, and photosynthetic pigment contents). The physical and chemical characteristics of growth media and plant growth were best with a medium containing 70% CGW and were better in a medium with 100% CGW than in one with 100% peat media. These results indicate that CGW is a viable alternative to peat for the cultivation of Calathea insignis.

Spent mushroom waste as a media replacement for peat moss in Kai-Lan (Brassica oleracea var. Alboglabra) production

Peat moss (PM) is the most widely used growing substrate for the pot culture. Due to diminishing availability and increasing price of PM, researchers are looking for viable alternatives for peat as a growth media component for potted plants. A pot study was conducted with a view to investigate the possibility of using spent mushroom waste (SMW) for Kai-lan (Brassica oleracea var. Alboglabra) production replacing peat moss (PM) in growth media. The treatments evaluated were 100% PM (control), 100% SMW, and mixtures of SMW and PM in different ratios like 1 : 1, 1 : 2, and 2 : 1 (v/v) with/without NPK amendment. The experiment was arranged in a completely randomized design with five replications per treatment. Chemical properties like pH and salinity level (EC) of SMW were within the acceptable range of crop production but, nutrient content, especially nitrogen content was not enough to provide sufficient nutrition to plant for normal growth. Only PM (100%) and SMW and PM mixture in 1 : 1 ratio with NPK amendment performed equally in terms of Kai-lan growth. This study confirms the feasibility of replacing PM by SMW up to a maximum of 50% in the growth media and suggests that NPK supplementation from inorganic sources is to ensure a higher productivity of Kai-lan.

Greenhouse gas (GHG) emissions from soils amended with digestate derived from anaerobic treatment of food waste

RATIONALE

The application of organic materials to agricultural lands is considered good practice to improve soil organic matter content and recycle nutrients for crop growth. The anaerobic treatment of food waste may have environmental benefits, particularly with regard to greenhouse gases (GHGs) mitigation and enhancement of carbon sequestration.

METHODS

This work presents the results from a field experiment to evaluate CO(2) , CH(4) and N(2) O emissions from grassland amended with digestate produced by anaerobic fermentation of food waste. Experimental plots, located close to Rothamsted Research-North Wyke, were established using a randomized block design with three replicates and two treatments, added digestate (DG) and the unamended control (CNT). The digestate was applied on three occasions at an equivalent rate of 80 kg N ha(-1) .

RESULTS

The application of digestate led to an increase in CO(2) emissions, especially after the 2(nd) application (74.1 kg CO(2) -C ha(-1)  day(-1) ) compared with the CNT soil (36.4 kg CO(2) -C ha(-1)  day(-1) ), whereas DG treatment did not affect the overall CH(4) and N(2) O emissions. The total grass yield harvested on a dry matter basis was greater in the DG treated plots (0.565 kg m(-2) ) than in the CNT plots (0.282 kg m(-2) ), as was the (15)  N content in the harvest collected from the DG plots.

CONCLUSIONS

The results suggest that the digestate can be applied to agricultural land as a fertilizer to grow crops. Our study was conducted in an exceptionally dry growing season, so conclusions about the effect of digestate on GHG emissions should take this into account, and further field trials conducted under more typical growing seasons are needed.

Growth responses of crop and weed species to heavy metals in pot and field experiments

Greenhouse and field studies were performed to examine the growth responses and possible phytoremediation capacity towards heavy metals of several Brassicaceae (Brassica alba, Brassica carinata, Brassica napus and Brassica nigra) and Poaceae (durum wheat and barley). Soils used featured total concentrations of Cr, Cu, Pb and Zn largely exceeding the maximum levels permitted by the Italian laws. Different organic amendments were tested such as a compost and the plant growth-promoting rhizobacterium Bacillus licheniformis. In the greenhouse experiment, plant length, leaf area index and shoots dry matter were evaluated periodically for the Brassicaceae examined. Whereas plant length, grains production, weight of 1,000 seeds, ear fertility and tiller density were determined under field conditions at the end of the crop cycle for wheat and barley. In general, the species tested appeared to be tolerant to high heavy metal concentrations in soil, and slightly significant differences were found for all parameters considered. A marked growth increase was shown to occur for Brassicaceae cultivated on compost- and bacillus-amended contaminated soils, with respect to non-amended contaminated soils. With some exception, higher growth parameters were measured for wheat and barley plants cropped from contaminated soils in comparison to non-contaminated soils. Further, bacillus amendment enhanced the length of wheat and barley plants in both non-contaminated and contaminated soils, while different effects were observed for the other parameters evaluated.

Evaluation of wastewater treatment by-products as soil amendment: Growth of sorghum-sudan grass and trace elements concentrations

Wastewater treatment by-products (WTBP), such as sewage sludge (SS) may be used to enhance soil chemical, physical, and biological properties. These enhanced soil properties, in turn, could from its source of production to its site of application. These concerns may be mitigated by incineration of the SS to produce ash (SSA) and dissolved in water and stored in ponds as contribute to an increase in plant growth, production, mineral nutrition. Some SS is difficult to handle due to bad odor in its raw state and has large mass, hence expensive for transportation weathered SSA (WSSA). A greenhouse study was conducted using Candler fine sand CFS; (CFS; pH = 6.8) and Ogeechee loamy sand OLS; (pH = 5.2) with application of either 0, 24.7, 49.4, 98.8, or 148.2 Mg ha(-1) as either SS, SSA, or WSSA to evaluate the biomass production and elemental composition responses of sorghum-sudan grass (Sorghum vulgaris var. Sudanese hitche). Shoot and root biomass were 2 to 3 fold greater in the soil amended with SS, than either SSA or WSSA. Concentrations of nutrient and trace elements in the shoots and roots increased with increasing rates of amendments. Application of these by-products up to 98.8 Mg ha(-1) rate did not adversely affect growth or accumulation of trace elements in sorghum-sudan grass. Long-term field studies are recommended to investigate the potential leaching of various elements from the amended soils in addition to evaluation of plant growth and production responses to determine the acceptable rates of these by-products as amendments to agricultural soils.

Development of sewage sludge-based synthetic aggregates for containerized ornamentals

Potential utilization of synthetic aggregates (SAs) developed from sewage sludge (SS) as a component of containerized media for French marigold (Tagetes patula) cultivation as a peat substitution was investigated in this study. The six different containerized media utilized were: peat only, SA 20%: peat 80%, SA 40%: peat 60%, SA 60%: peat 40%, SA 80%: peat 20% and SA only. The physical and chemical characteristics of all media were determined. SA-based media showed higher pH, electrical conductivity (EC), bulk density, particle density and nutrient contents (N, P, Ca and Mg) compared to peat media. The highest plant length, number of flowers per plant, shoot fresh weight, shoot dry weight, root length, root fresh weight and root dry weight obtained from the medium having SA 40%: peat 60% increased by 13.69%, 23.53%, 41.46%, 58.95%, 2.43%, 39.09% and 21.68%, respectively, compared to the peat control. The addition of 60% and 100% of SAs to the growth media gave the lowest growth and yield parameters compared to the peat control due to their high EC and pH. Plant tissues obtained from media with added SAs showed increased N, P, Ca and Mg contents compared to plant tissues obtained from peat media. Media with added SAs did not significantly increase concentrations of Cu, Cd, Cr and Pb in plant tissues but the Zn concentration was significantly increased. SA addition to media did not pose any phytotoxicity risks in French marigold plants. SAs can be suggested as viable potting media components to substitute for the widely used and more expensive peat utilized in horticulture.

A risk-based decision tool for the management of organic waste in agriculture and farming activities (FARMERS)

Currently, specific management guidelines must be implemented for guaranteeing the safe reuse of organic waste in agriculture. With that aim, this work was focused on the development of a decision support tool for a safe and sustainable management of cattle manure as fertiliser in pastureland, to control and limit metal accumulation in soil and to reduce metal biotransfer from soil to other compartments. The system was developed on the basis of an environmental risk assessment multi-compartmental model. In contrast to other management tools, a long-term dynamic modelling approach was selected considering the persistence of metals in the environment. A detailed description of the underlying flow equations which accounts for distribution, human exposure and risk characterisation of metals in the assessed scenario was presented, as well as model parameterization. The tool was implemented in Visual C++ and is structured on a data base, where all required data is stored, the risk assessment model and a GIS module for the visualization of the scenario characteristics and the results obtained (risk indexes). The decision support system allows choosing among three estimation options, depending on the needs of the user, which provide information to both farmers and policy makers. The first option is useful for evaluating the adequacy of the current management practices of the different farms, and the remaining ones provides information on the measures that can be taken to carry out a fertilising plan without exceeding risk to human health. Among other results, maximum values of application rates of manure, maximum permissible metal content of manure and maximum application times in a particular scenario can be estimated by this system. To illustrate tool application, a real case study with data corresponding to different farms of a milk production cooperative was presented.

Screening Capsicum chinense fruits for heavy metals bioaccumulation

Elevated concentrations of heavy metals in edible plants could expose consumers to excessive levels of potentially hazardous chemicals. Sixty-three accessions (genotypes) of Capsicum chinense Jacq, collected from 8 countries of origin were grown in a silty-loam soil under field conditions. At maturity, fruits were collected and analyzed for seven heavy metals (Cd, Cr, Ni, Pb, Zn, Cu, and Mo) concentrations. The main objectives of this investigation were: 1) to determine the concentrations of seven heavy metals in the soil and monitor their accumulation in mature fruits, 2) to categorize the pepper accessions as low or high heavy metal accumulators, and 3) to determine if heavy metal content of the pepper fruit was lower than the permitted limits. Concentrations and relative proportions of heavy metals in pepper fruits of C. chinense varied among accessions. Fruits of Plant Introduction (PI) 355820 accumulated significant concentrations of Cd (0.47 μg g(-1) dry fruit). PI-260522 accumulated the highest concentration of Pb (2.12 μg g(-1) dry fruit) among the 63 accessions tested. This accession (PI-260522) contained about twice the Pb limit on a fresh weight basis. Among the 63 accessions analyzed, PI-238051 contained the highest levels of Ni (17.2 μg g(-1)). We concluded that high accumulator genotypes may be useful for phytoremediation, while, low accumulator accessions might be appropriate selections for growing on Cd-, Pb-, or Ni-contaminated soils to prevent potential human exposure to heavy metals and health hazards through the food chain.

Leaching composted lignocellulosic wastes to prepare container media: feasibility and environmental concerns

The leaching of salt and mineral elements from three composts prepared with residual vegetable crop biomass (melon, pepper or zucchini) was studied using methacrylate columns and distilled water. The benefits of the leached composts to be used for ornamental potted plant production were also analysed. After leaching 5 container capacities of effluent, both the electrical conductivity and the concentration of soluble mineral elements in compost leachates decreased substantially and remained close to the target levels. Composts reacted differently to leaching due to differences in the raw waste sources and the composting process and hence, in their physical and chemical characteristics. At the end of the experiment, after pouring 8 container capacities of water, the leaching efficiency of the salts was 96%, 93% and 87% for melon, pepper and zucchini-based composts, respectively. Mineral elements differed in their ability to be removed from the composts; N (NH(4)(+) and NO(3)(-)), K(+), Na(+), Cl(-), and SO(4)(2-) were leached readily, whereas H(2)PO(4)(-), Ca(2+), and Mg(2+) were removed hardly. Leached composts showed a range of physico-chemical and chemical characteristics suitable for use as growing media constituents. Potted Calendula and Calceolaria plants grew in the substrates prepared with the leached composts better than in those made with the non-leached ones. Finally, special emphasis must be paid to the management of the effluents produced under commercial conditions to avoid environmental pollution.

Growth, yield, and fruit quality of pepper plants amended with two sanitized sewage sludges

Organic wastes such as sewage sludge have been successfully used to increase crop productivity of horticultural soils. Nevertheless, considerations of the impact of sludges on vegetable and fruit quality have received little attention. Therefore, the objective of the present work was to investigate the impact of two sanitized sewage sludges, autothermal thermophilic aerobic digestion (ATAD) and compost sludge, on the growth, yield, and fruit quality of pepper plants ( Capsicum annuum L. cv. Piquillo) grown in the greenhouse. Two doses of ATAD (15 and 30% v/v) and three of composted sludge (15, 30, and 45%) were applied to a peat-based potting mix. Unamended substrate was included as control. ATAD and composted sludge increased leaf, shoot, and root dry matter, as well as fruit yield, mainly due to a higher number of fruits per plant. There was no effect of sludge on fruit size (dry matter per fruit and diameter). The concentrations of Zn and Cu in fruit increased with the addition of sewage sludges. Nevertheless, the levels of these elements remained below toxic thresholds. Pepper fruits from sludge-amended plants maintained low concentrations of capsaicin and dihydrocapsaicin, thus indicating low pungency level, in accordance with the regulations prescribed by the Control Board of "Lodosa Piquillo peppers" Origin Denomination. The application of sludges did not modify the concentration of vitamin C (ASC) in fruit, whereas the highest doses of composted sludge tended to increase the content of reduced (GSH) and oxidized (GSSG) glutathione, without change in the GSH/GSSG ratio. There were no effects of sludge on the transcript levels of enzymes involved in the synthesis of vitamin C, l-galactono-1,4-lactone dehydrogenase (GLDH) or in the ascorbate-glutathione cycle, ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), and glutathione reductase (GR). Results suggest that the synthesis and degradation of ASC and GSH were compensated for in most of the treatments assayed. The application of sanitized sludges to pepper plants can improve pepper yield without loss of food nutritional quality, in terms of fruit size and vitamin C, glutathione, and capsaicinoid contents.

Sewage sludge sugarcane trash based compost and synthetic aggregates as peat substitutes in containerized media for crop production

Effect of partial substitution of peat in growth media by sewage sludge sugarcane trash based compost (SSC) and synthetic aggregates (SA) on the physical and chemical characteristics of the growth media and on the growth and nutrition of lettuce (Lactuca sativa L.) grown in the substituted media was investigated under this study. SSC was produced from sugarcane trash and sewage sludge. Unconventional SA were produced by low productive acidic red soil with paper waste and starch waste. The treatments assayed were: SSC (40%)+Peat (60%), SA (40%)+Peat (60%), SSC (60%)+SA (40%), SSC (40%)+SA (20%)+Peat (40%) and SSC (40%)+SA (40%)+Peat (20%). Peat only was used as the control. The physical and chemical properties of all growing media were analyzed. SSC-SA based substrates showed adequate physical and chemical properties compared to peat for their use as growing media in horticulture. In relation to the plant growth in peat control, plants grown in the SSC-SA based substrates reached better growth and nutrition. The concentration of trace elements in plant tissues was far lower than the ranges considered phytotoxic for plants. Utilization of SSC and SA can be considered as an alternative media component to substitute the widely using expensive peat in horticulture.

The potential of near infrared reflectance spectroscopy (NIRS) for the estimation of agroindustrial compost quality

Composting is an environmentally friendly alternative for the recycling of organic wastes and its use is increasing in recent years. An exhaustive monitoring of the composting process and of the final compost characteristics is necessary to certify that the values of compost characteristics are within the limits established by the legislation in order to obtain a safe and marketable product. The analysis of these parameters on each composting batch in the commercial composting plant is time-consuming and expensive. So, their estimation in the composting facilities based on the use of near infrared reflectance spectroscopy (NIRS) could be an interesting approach in order to monitor compost quality. In this study, more than 300 samples from 20 different composting procedures were used to calibrate and validate the NIRS estimation of compost properties (pH, electrical conductivity (EC), total organic matter (TOM), total organic carbon (TOC), total nitrogen (TN) and C/N ratio, macronutrient contents (N, P, K) and potentially pollutant element concentrations (Fe, Cu, Mn and Zn)). The composts used were elaborated using different organic wastes from agroindustrial activities (GS: grape stalk; EGM: exhausted grape marc; GM: grape marc; V: vinasse; CJW: citrus juice waste; Alpeorujo: olive-oil waste; AS: almond skin; EP: exhausted peat; TSW: tomato soup waste; SMS: spent mushroom substrate) co-composted with manures (CM: cattle manure; PM: poultry manure) or urban wastes (SS: sewage sludge) The estimation results showed that the NIRS technique needs to be fitted to each element and property, using specific spectrum transformations, in order to achieve an acceptable accuracy in the prediction. However, excellent prediction results were obtained for TOM and TOC, successful calibrations for pH, EC, Fe and Mn, and moderately successful estimations for TN, C/N ratio, P, K, Cu and Zn.

Utilisation of manure composts by high-value crops: safety and environmental challenges

The intensification in livestock production has increased the need of efficient treatments of waste streams especially to preserve as much as possible, the nutrients into the soil-plant system. Composting is a cheap, efficient and sustainable treatment for solid wastes that is always included in any manure treatment scenario. In this paper, an overview about the environmental and safety challenges of composting of manures is made considering the compost quality requirements established by the main demanding sectors. Co-composting and additive strategies are presented as feasible options for the improvement of compost quality. For quality evaluation of manure compost, the use of both classical and innovative instrumental techniques could increase our knowledge about added properties in compost, especially those related to organic matter stability.

Spent mushroom substrates as component of growing media for germination and growth of horticultural plants

This research work was conducted in order to investigate the possibility of using spent mushroom substrate (SMS) in the production of horticultural seedlings replacing part of the peat in the growing media. Three vegetable species with different salt sensitivities, the less sensitive being tomato (Lycopersicon esculentum var. Muchamiel), the moderately salt-sensitive being courgette (Cucurbita pepo L. var. Afrodite F1) and the most salt-sensitive being pepper (Capsicum annum L. var. Lamuyo F1) were grown in 12 media containing SMS of two types of mushroom (Agaricus bisporus (SMS-AB) and Pleurotus ostreatus (SMS-PO)) or a mixture of both 50% (v/v) (SMS-50), as well as peat in various ratios. The proportions of each residue in the mixtures elaborated with peat were 25%, 50%, 75% and 100% v/v residue. A substrate of 100% peat was used as control. The experiment was arranged in a completely-randomised design with two replicates per treatment under greenhouse conditions. Prior to sowing, some physical, physico-chemical and chemical properties of the growing media were determined and seed germination and fresh weight of seedling were also measured. In most of the cases, the addition of SMS to the growing media produced an increase in the pH values, salt contents, macro and micronutrient concentrations and a decrease in the water holding capacity contents in comparison to peat, whereas great differences were found in the air capacity values between SMS-based substrates and peat. Up to 75% SMS can be used in mixtures with peat for seed germination of the plant species studied. Regarding the most suitable SMS-based substrates for plant growth, any substrate could be used for tomato seedling production. However, all SMS-AB-based substrates and the media containing low dose of SMS-PO and SMS-50 were adequate for growth of courgette and pepper.

Emission of CO2 and N2O from soil cultivated with common bean (Phaseolus vulgaris L.) fertilized with different N sources

Addition of different forms of nitrogen fertilizer to cultivated soil is known to affect carbon dioxide (CO(2)) and nitrous oxide (N(2)O) emissions. In this study, the effect of urea, wastewater sludge and vermicompost on emissions of CO(2) and N(2)O in soil cultivated with bean was investigated. Beans were cultivated in the greenhouse in three consecutive experiments, fertilized with or without wastewater sludge at two application rates (33 and 55 Mg fresh wastewater sludge ha(-1), i.e. 48 and 80 kg N ha(-1) considering a N mineralization rate of 40%), vermicompost derived from the wastewater sludge (212 Mg ha(-1), i.e. 80 kg N ha(-1)) or urea (170 kg ha(-1), i.e. 80 kg N ha(-1)), while pH, electrolytic conductivity (EC), inorganic nitrogen and CO(2) and N(2)O emissions were monitored. Vermicompost added to soil increased EC at onset of the experiment, but thereafter values were similar to the other treatments. Most of the NO(3)(-) was taken up by the plants, although some was leached from the upper to the lower soil layer. CO(2) emission was 375 C kg ha(-1) y(-1) in the unamended soil, 340 kg C ha(-1) y(-1) in the urea-amended soil and 839 kg ha(-1) y(-1) in the vermicompost-amended soil. N(2)O emission was 2.92 kg N ha(-1) y(-1) in soil amended with 55 Mg wastewater sludge ha(-1), but only 0.03 kg N ha(-1) y(-1) in the unamended soil. The emission of CO(2) was affected by the phenological stage of the plant while organic fertilizer increased the CO(2) and N(2)O emission, and the yield per plant. Environmental and economic implications must to be considered to decide how many, how often and what kind of organic fertilizer could be used to increase yields, while limiting soil deterioration and greenhouse gas emissions.

Fertilization of Pinus pinea L. seedlings with a sewage sludge-based compost

Two experiments were conducted to evaluate the effect of a sewage sludge-based compost (SSC) on the growth and mineral composition of containerized Pinus pinea L. seedlings. In the first experiment, five different substrates were tested: four binary mixtures of SSC and peat (100% SSC, 75% SSC, 50% SSC and 25% SSC, by volume) without fertilization, and a control substrate (peat-based substrate + fertilizer). Seedlings growing in the 100% SSC substrate showed the lowest growth, a consequence of both the low water availability and the high electrical conductivity that made SSC unsuitable to be the only component of a growing-media for pine ;seedlings'. The 50% SSC substrate presented physical and chemical properties similar to the control substrate and near the acceptable range for a growing-media. Moreover, no significant differences were found between growth of seedlings from treatment 50% SSC (without mineral fertilization) and seedlings from control treatment (with mineral fertilization). In the second experiment, a fertilization assay was performed with two substrates selected from the first experiment (50% SSC and control). The two substrates were fertilized with three levels of a macronutrient fertilizer (0.5, 1.0 and 2.0 g L( -1)) and two levels of a micronutrient fertilizer (0 and 0.4 g L(-1) of fertilizer containing only micronutrients). Results obtained suggest that replacing 50% (by volume) of peat-based substrate by the sewage sludge-based compost allowed: maintenance of the commercial value of seedlings; reduction of the amount of peat used in the substrate; a need for only half the amount of macronutrient fertilizer applied in the basal fertilization; and omission of micronutrient fertilization.

Substitution of peat for municipal solid waste- and sewage sludge-based composts in nursery growing media: effects on growth and nutrition of the native shrub Pistacia lentiscus L

In this study, the effect of a partial substitution of peat for compost on the growth and nutrition of a native shrub (Pistacia lentiscus L.) was tested. Composts were prepared from pruning and municipal solid wastes or pruning waste and sewage sludge. For preparing growing media each compost was added at a rate of 40%, fresh pine bark at 20% or 40% and peat at 20%, 40% or 60%. Aqueous extracts from the substrates did not impair germination of cress (germination bioassay). In relation to plants growing in peat-based substrate (used as a control), plants of the compost-based substrates reached better growth and nutrition, especially when using the sewage sludge-based compost, and the P uptake was notably enhanced. The concentrations of trace elements were far lower than the ranges considered phytotoxic for vascular plants. Detrimental effect derived from using fresh pine bark was not observed.

Study of biochemical and microbiological parameters during composting of pine and eucalyptus bark

To study the possibility of some residues from pulp and paper industry being used as substrates to produce seedlings in containers, three composting experiments were carried out using eucalyptus bark, pine bark and a mixture (60:40, v:v) of pine bark+eucalyptus bark. Biochemical parameters studied were: acid and alkaline phosphatases, lipase (C10), protease, urease, beta-glucosidase and total cellulases. The microbiological populations of total aerobic bacteria, total fungi, actinomycetes, nitrifying bacteria, cellulolytic bacteria and fungi were also evaluated. At the end of the process physicochemical characterization of composts was also performed. Results showed in general that the highest microbiological populations as well as for enzymatic activities occurred during the thermophilic phase (>40 degrees C) of the process. On the other hand and according to the physicochemical characteristics of composts pine bark is the most appropriate material to be used in the formulation of substrates to produce plants in containers.

Evaluation of composted sewage sludge (CSS) as a soil amendment for Bermudagrass growth

In order to evaluate the growth of Bermudagrass (Cynodon dactylon L.) in soils amended with 5-100% composted sewage sludge (CSS) and the impacts of CSS amendment on soil physical and chemical properties an experiment was conducted. Soils amended with < or = 20% CSS did not significantly affect the seedling emergence, while the contents of chlorophyll, nitrogen, phosphorous and potassium of Bermudagrass grown in such soils were greatly improved. Bulk density, water retention and nutrient contents of the soil were also improved with the amendment of CSS, but high CSS contents introduced excessive amounts of heavy metals and soluble salts. Results show that Cu, Zn and Pb accumulated slightly (up to approximately 2.3 times) in clippings of Bermudagrass grown in CSS-amended soils compared to those grown in the base and reference soils, while no significant Cd absorption in shoots of Bermudagrass occurred. The detrimental effects on seedling emergence and turfgrass growth observed on substrates with high (> or = 40%) CSS contents were mainly attributed to the presence of high soluble salt concentrations. The findings suggest that addition of CSS at 10-20% levels can greatly improve the soil nutrient supply for turfgrass growth without significantly affecting heavy metal and soluble salt contents of the soil.

Effects of two sludge application on fractionation and phytotoxicity of zinc and copper in soil

The potential harm of heavy metals is a primary concern in application of sludge to the agricultural land. A pot experiment was conducted to evaluate the effect of two sludges on fractionation of Zn and Cu in soil and their phytotoxicity to pakchoi. The loamy soil was mixed with 0%, 20%, 40%, 60% and 80% (by weight) of digested sewage sludge (SS) and composted sludge (SC). The additions of the both sludges caused a significant raise in all fractions, resulting in that exchangeable (EXCH) and organic matter (OM) became predominance for Zn and organic bound Cu occupied the largest portion. There was more available amount for Zn and Cu in SS treatments than SC treatments. During the pot experiment, the concentration of Zn in EXCH, carbonate (CAR) and OM and Cu in EXCH and OM fractions decreased in all treatments, so their bioavailability reduced. Germination rate and plant biomass decreased when the addition rate was high and the best yield appeared in 20% mixtures at the harvest of pakchoi. The two sludges increased tissue contents of Zn and Cu especially in the SS treatments. Zn in pakchoi was not only in relationship to deltaEXCH and deltaCAR forms but also in deltaOM forms in the sludge-soil mixtures. Tissue content of Cu in pakchoi grown on SC-soils could not be predicted by deltaEXCH. These correlation rates between Zn and Cu accumulation in pakchoi and variation of different fractions increased with time, which might indicate that sludges represented stronger impacts on the plant in long-term land application.

Application of cattle manure as fertilizer in pastureland: estimating the incremental risk due to metal accumulation employing a multicompartment model

Specific-site data of metal concentration in cattle manure from NW Spain and a multicompartment fate and exposure model were used to evaluate metal fate and the main routes of exposure after a 100 year period of application of cattle manure as fertiliser in pastureland. Risk assessment was performed as a probabilistic analysis, and using a conservative worst-case exposure scenario. An accumulation model was used to predict the metal concentration in each environmental medium of concern. The incremental risk was estimated for the population inhabiting the surroundings of the area by a general multiexposure model. Monte Carlo simulations were performed to analyse uncertainty of the results. Furthermore, a sensitivity analysis was carried out to identify the contribution to variance by the different metals and exposure routes. Among the five pathways evaluated, the ingestion of meat and milk from cattle grazing in the area represents the main contribution to total exposure. The results indicate that the incremental risk to human health for people living in the surroundings of pasturelands due to continuous application of cattle manure after a 100 year period are not negligible for the metals considered (Cd, Cu, Ni, Pb and Zn), posing a total Reasonable Maximum Exposure (RME) of 0.75, being the ingestion of meat the main exposure pathway.