Application of ceramsite and activated alumina balls as recyclable bulking agents for sludge composting

Recent advances in swine wastewater treatment technologies for resource recovery: A comprehensive review

Swine wastewater (SW), characterized by highly complex organic and nutrient substances, poses serious impacts on aquatic environment and public health. Furthermore, SW harbors valuable resources that possess substantial economic potential. As such, SW treatment technologies place increased emphasis on resource recycling, while progressively advancing towards energy saving, sustainability, and circular economy principles. This review comprehensively encapsulates the state-of-the-art knowledge for treating SW, including conventional (i.e., constructed wetlands, air stripping and aerobic system) and resource-utilization-based (i.e., anaerobic digestion, membrane separation, anaerobic ammonium oxidation, microbial fuel cells, and microalgal-based system) technologies. Furthermore, this research also elaborates the key factors influencing the SW treatment performance, such as pH, temperature, dissolved oxygen, hydraulic retention time and organic loading rate. The potentials for reutilizing energy, biomass and digestate produced during the SW treatment processes are also summarized. Moreover, the obstacles associated with full-scale implementation, long-term treatment, energy-efficient design, and nutrient recovery of various resource-utilization-based SW treatment technologies are emphasized. In addition, future research prospective, such as prioritization of process optimization, in-depth exploration of microbial mechanisms, enhancement of energy conversion efficiency, and integration of diverse technologies, are highlighted to expand engineering applications and establish a sustainable SW treatment system.

Optimization of organic solid waste composting process through iron-related additives: A systematic review

Composting is an environmentally friendly method that facilitates the biodegradation of organic solid waste, ultimately transforming it into stable end-products suitable for various applications. The element iron (Fe) exhibits flexibility in form and valence. The typical Fe-related additives include zero-valent-iron, iron oxides, ferric and ferrous ion salts, which can be targeted to drive composting process through different mechanisms and are of keen interest to academics. Therefore, this review integrated relevant literature from recent years to provide more comprehensive overview about the influence and mechanisms of various Fe-related additives on composting process, including organic components conversion, humus formation and sequestration, changes in biological factors, stability and safety of composting end-products. Meanwhile, it was recommended that further research be conducted on the deep action mechanisms, biochemical pathways, budget balance analysis, products stability and application during organic solid waste composting with Fe-related additives. This review provided guidance for the subsequent targeted application of Fe-related additives in compost, thereby facilitating cost reduction and promoting circular economy objectives.

Review of inventory data for the biological treatment of sewage sludge

The biological treatment of municipal sewage sludge, including anaerobic digestion and composting, was reviewed with the purpose of establishing inventory data to address all the inputs and outputs related to sludge treatment. We identified 193 scientific papers, resulting in 64 datasets on anaerobic digestion and 35 datasets on composting. For anaerobic digestion, biogas production varied significantly (up to a factor of four) depending on the sludge. A useful correlation was identified between the amount of methane produced and the degradation of volatile solids. According to statistical tests, no significant differences were found in biogas production for mesophilic and thermophilic digesters. In addition, methane content varied significantly, and very few data were available for digestate composition or for energy consumption and recovery. For composting, accurate estimates relating to the degradation of sewage sludge could not be made, since organic bulking materials were part of the final composted product. Data on emissions to air are currently scarce, which points to the need for more published information. The inventory data evaluated herein are useful in the feasibility assessment of the biological treatment of sewage sludge, for comparing technologies, for example in LCA studies and as a basis for evaluating the performance of a specific biological sludge treatment plant. However, a great deal of the reviewed data originated from laboratory and pilot-scale studies, and so there is a need for more complete datasets on the performance of full-scale technologies, in order to establish full inventories and identify differences in technologies and operational conditions.

Effects of initial particle sizes of Triarrhena lutarioriparia on processing performance, material properties, and heavy metal speciation in sewage sludge composting

The purpose of this study was to investigate the effect of initial particle size (IPS) on the environmental parameters and heavy metal speciation during sludge composting. Three piles were conducted: fine material (FM, screen underflow), coarse material (CM, oversize product), and mixed material (MM, mix FM and CM in 1:1). Results showed that the temperature trends of the three piles in different layers were highly repeatable during the thermophilic period. With the decrease of IPS, the heating rate and the highest temperature of the pile increased, the thermophilic period was prolonged, and the highest temperature area in the pile shifted to a lower layer. It also promoted the organic matter degradation, compost maturation, and nitrogen fixation effect. Composting had a good effect on the passivation of heavy metals, especially Cd, Cu, and Pb. The passivation effect on Cd and Cu was FM > CM > MM, and on Pb was CM > FM > MM. Fourier transform infrared spectroscopy, excitation-emission matrix, and thermogravimetric thermal analysis indicated that FM had the highest content of aromatic structure and humic-like substance on D40. The redundancy analysis revealed that MM was beneficial to improve the internal uniformity during composting.

Insights into the effect mechanism of back-mixing inoculation on sewage sludge biodrying process: Biodrying characteristics and microbial community succession

Back mixing was frequently used to replace conventional bulking agenting, however, however, the internal effect mechanism was unclear. This study compared four bulking agents: mushroom residue (MR), MR + primary BM (BM-P), BM-P, and secondary BM (BM-S). The effect mechanism of back mixing (BM) inoculation was assessed based on biodrying performance and microbial community succession. Four trials (Trial A, Trial B, Trial C, and Trial D) reached maximum temperatures of 61.9, 68.8, 73.7, and 69.9 °C on days 6, 3, 2, and 2, respectively. Application of BM increased pile warming rate and resulted in higher temperatures. Temperature changes and microbial competition lead to decline in microbial diversity and richness during the biodrying process. Microbial diversity increased of four biodried products. The number of microorganisms shared by Trial A, Trial B, Trial C, and Trial D were 90, 119, 224, and 300, respectively. The addition of BM improved microbial community stability, and facilitating the initiation of biodrying process. Microbial genera that played an important role in the biodrying process included Ureibacillus, Bacillus, Sphaerobacter, and Tepidimicrobium. Based on these results, it was concluded that BM was efficient method to enhanced the microbial activity and reduced the usage of bulking agent.

Biostimulation of Petroleum-Contaminated Soil Using Organic and Inorganic Amendments

The most common approaches for the in-situ bioremediation of contaminated sites worldwide are bioaugmentation and biostimulation. Biostimulation has often proved more effective for chronically contaminated sites. This study examined the effectiveness of optimized water hyacinth compost in comparison with other organic and inorganic amendments for the remediation of crude oil-polluted soils. Water hyacinth was found to be rich in nutrients necessary to stimulate microbial growth and activity. An organic geochemical analysis revealed that all amendments in this study increased total petroleum hydrocarbon (TPH) biodegradation by ≥75% within 56 days, with the greatest biodegradation (93%) occurring in sterilized soil inoculated with optimized water hyacinth compost. This was followed by polluted soil amended with a combination of spent mushroom and water hyacinth composts (SMC + WH), which recorded a TPH biodegradation of 89%. Soil amendment using the inorganic fertilizer NPK (20:10:10) resulted in 86% TPH biodegradation. On the other hand, control samples (natural attenuation) recorded only 4% degradation. A molecular analysis of residual polycyclic aromatic hydrocarbons (PAHs) showed that the 16 PAHs designated by the US EPA as priority pollutants were either completely or highly degraded in the combined treatment (SMC + WH), indicating the potential of this amendment for the environmental remediation of soils contaminated with recalcitrant organic pollutants.

An Alternative to Vermiculite: Composting on Tropical Islands Using Coral Sand to Enhance Nitrogen Retention during Ventilation

Reducing nitrogen loss during composting with forced ventilation was comprehensively investigated in this study. Coral sand was tailored in the co-composting in the co-composting of sludge and litters. The physicochemical results revealed that forced ventilation prolonged the thermophilic phase and accelerated the substrate decomposition. With the addition of 10% native coral sand, the amount of nitrogen loss decreased by 9.2% compared with the original group. The microbial community evaluation revealed that the effect of forced ventilation on colony abundance was significantly greater than that of adding coral sand. This study demonstrated that when composting on a tropical island, adding coral sand under forced ventilation was a viable solution for realizing sustainable development.

Effects of different additives and aerobic composting factors on heavy metal bioavailability reduction and compost parameters: A meta-analysis

Additives are considered a promising approach to accelerate the composting process and alleviate the dissemination of pollutants to the environment. However, nearly all previous articles have focused on the impact of additive amounts on the reduction of HMs, which may not fully represent the main factor shaping HMs bioavailability status during composting. Simultaneously, previous reviews only explored the impacts, speciation, and toxicity mechanism of HMs during composting. Hence, a global-scale meta-analysis was conducted to investigate the response patterns of HMs bioavailability and compost parameters to different additives, composting duration, and composting factors (additive types, feedstock, bulking agents, and composting methods) by measuring the weighted mean values of the response ratio "[ln (RR)]" and size effect (%). The results revealed that additives significantly lessened HMs bioavailability by ≥ 40% in the final compost products than controls. The bioavailability decline rates were -40%, -60%, -57%, -55%, -42%, and -44% for Zn, Pb, Ni, Cu, Cr, and Cd. Simultaneously, additives significantly improved the total nitrogen (TN) (+16%), pH (+5%), and temperature (+5%), and decreased total organic carbon (TOC) (-17%), moisture content (MC) (-18%), and C/N ratio (-19%). Furthermore, we found that the prolongation of composting time significantly promoted the effect of additives on declining HMs bioavailability (p < 0.05). Nevertheless, increasing additive amounts revealed an insignificant impact on decreasing the HMs bioavailability (p > 0.05). Eventually, using zeolite as an additive, chicken manure as feedstock, sawdust as a bulking agent, and a reactor as composting method had the most significant reduction effect on HMs bioavailability (p < 0.05). The findings of this meta-analysis may contribute to the selection, modification, and application of additives and composting factors to manage the level of bioavailable HMs in the compost products.

A comprehensive review on the decontamination of lead(ii) from water and wastewater by low-cost biosorbents

The disadvantages of conventional methods in water and wastewater management including the demand for high energy consumption, the creation of secondary toxic sludge, and operation cost are much too high for developing countries. However, adsorption using low-cost biosorbents is the most efficient non-conventional technique for heavy metals removal. The high adsorption capacities, cost-effectiveness, and the abundance of agricultural waste materials in nature are the important parameters that explain why these biosorbents are economical for heavy metals removal. The present investigation sought to review the biosorption of lead [Pb(ii)] onto low-cost biosorbents to understand their adsorption mechanism. The review shows that biosorption using low-cost biosorbents is eco-friendly, cost-effective, and is a simple technique for water and wastewater treatment containing lead(ii) ions. The batch biosorption tests carried out in most studies show that Pb(ii) biosorption by the low-cost biosorbents is dependent on biosorption variables such as pH of the aqueous solution, contact time, biosorbent dose, Pb(ii) initial concentration, and temperature. Furthermore, batch equilibrium data have been explored in many studies by evaluating the kinetics, isothermal and thermodynamic variables. Most of the studies on the adsorptive removal of Pb(ii) were found to follow the pseudo-second kinetic and Langmuir isotherm models with the thermodynamics variables suggesting the feasibility and spontaneous nature of Pb(ii) sequestration. However, gaps exist to increase biosorption ability, economic feasibility, optimization of the biosorption system, and desorption and regeneration of the used agricultural biosorbents.

Effects of H3PO4 modified biochar on heavy metal mobility and resistance genes removal during swine manure composting

In this research, static composting treatments of swine manure with forced ventilation were conducted to study the effects of biochar (BC) and H₃PO₄ modified biochar (BP) addition on heavy metals (HMs) stabilization, profiles of antibiotic resistance genes (ARGs), heavy metals resistance genes (MRGs) and bacterial communities during swine manure composting. After 42 days of the composting, compared to control (CK), BC and BP decreased the concentration of diethylenetriamine pentaacetic acid extractable Cu and Zn by 12.04%, 15.15% and 26.91%, 36.50%, respectively. Furthermore, BC and BP treatments reduced the total abundances of nine ARGs by 4.02% and 66.21%, and five MRGs by 53.66% and 58.81%, compared to CK in the compost product. Network analysis and square structural equation model analysis revealed that the decrease of ARGs and MRGs in BP treatment was related tothe change in bacterial community during the composting, rather than differences in co-selection pressure.

Effective removal of methylene blue dye from water with nanocomposite ceramsites in a fixed-bed column

The study aims to remove methylene blue dye from water with a fixed-bed column packed with Cu₂O nanocomposite ceramsites. The column showed the advantages of fixed-bed column adsorption and photocatalytic oxidation. The Cu₂O nanocomposite ceramsites with strong photocatalytic oxidation activity and well-developed porous structure were successfully prepared with the chemical vapour deposition process, which also met with the China's industrial standard of CJ/T 299-2008 and China's national standard of GB 5085.3-2007. In the column experiments under the experimental conditions (initial pH was 3, reaction temperature was 25°C and flow rate was 33 mL/min), the breakthrough curve was much more smooth. The breakthrough time and saturation time under ultraviolet radiation were 36.0% and 26.83% longer than those under the conditions without ultraviolet radiation, because the micro-pore structure of ceramsite was closely related to optical excitation properties of nano-Cu₂O. The Yoon-Nelson and Adams-Bohart models were applied to describe the obtained breakthrough curves using non-linear regression, in which the Yoon-Nelson model gave the better prediction results for breakthrough curves, with R²>0.98. Besides, amines were the dominant intermediates at saturation point and final products were inorganic anions. This study confirmed that the fixed-bed column packed with Cu₂O nanocomposite ceramsites could efficiently treat methylene blue dye wastewater, due to the structure-function relationship between ceramsite and nano-Cu₂O.

Simultaneous reductions in antibiotics and heavy metal pollution during manure composting

The co-existence of antibiotics and heavy metal (HM) is common in manure. However, existing strategies for improving antibiotic dissipation or HM immobilization during composting rarely consider their combined pollution. In this study, we used agricultural lime and a newly designed attapulgite-activated carbon composite (AACC) to enhance the stabilization of HMs in a pilot-scale swine manure composting system and assessed the effectiveness of these materials for removing antibiotic residues. Results indicated that the application of either lime or AACC simultaneously enhanced HM immobilization and antibiotic degradation. In particular, the addition of AACC reduced the enrichment of Cr, Cd, Pb, and As during composting and decreased the half-lives of the antibiotics from 10.7 days to 6.3 days, which were more effectively than lime. The physicochemical and microbiological responses to different additives were subsequently studied to understand the mechanisms underlying the fates of HMs and antibiotics. High HM stress in manure inhibited antibiotic dissipation, but metal immobilization alleviated this effect. The AACC accelerated HM immobilization by surface adsorption and metal precipitation, and this enhancement strengthened during the late composting stage due to an increase in pH, whereas lime exhibited a short-term effect. Moreover, the AACC addition enhanced the contribution of bacteria to changes in antibiotic concentrations, while the increase in pile temperature could be a major factor that contributed to the acceleration of antibiotic degradation after the addition of lime. Characterization of the final compost further showed that AACC-treated compost had the lowest residual concentrations of HMs and antibiotics, higher mortality of ascarid egg, improved nitrogen conversation, and reduced phytotoxicity. Thus, co-composting of swine manure with AACC is a promising approach for producing safer compost for use in agriculture.

Beer lees and ceramsite amendments enhance the two-stage co-composting of green waste

Composting is a major way to process green waste (GW), and amendments are important in GW composting. In this study of the two-stage co-composting of GW, beer lees (0, 25, 30%) and/or ceramsite (0, 10, 15%) were assessed as amendments. Changes in bulk density, porosity, temperature, pH, gaseous emissions, dissolved organic carbon (DOC) and nitrogen (DON), lignocellulose degradation, microbial abundances, and phytotoxicity were assessed during GW composting with the amendments. Treatments with a combination of beer lees and ceramsite had positive effects, and 25% beer lees and 15% ceramsite optimized all compost parameters. The optimal combination of amendments extended the thermophilic phase, enhanced the lignocellulose decomposition, and generated a stable and mature product in 20 days. Consequently, the best final compost was not phytotoxic (germination index: 164%), was mature (void space ratio: 48.48, pH: 7.20, and DOC/DON ratio: 0.51), and nutrient-rich (especially for N: 5.13%, P: 1.84%, and K: 0.68%).

Influence of reusable polypropylene packing on ammonia and greenhouse gas emissions during sewage sludge composting-a lab-scale investigation

Bulking agents are particularly important for sewage sludge composting. In this study, reusable polypropylene packing (RPP) was mixed with sawdust to improve composting. The effect of the mix ratio of sawdust and RPP on the physicochemical characteristics, nitrogen transformation, and emissions of greenhouse gas (GHG) as well as differences in the germination index values was detected in a lab-scale composting experiment. The results showed that the unique use of RPP as a bulking agent increased the moisture content over 70%, which resulted in poorer porosity and a less efficient O₂ utilization environment and thus suppressed the degradation of organic matter. The highest CH₄ 9275.8 mg and lowest CO₂ 202.6 g emissions were detected after 25 days of composting in the treatment with RPP used as a bulking agent. When the mixing ratio of sawdust and RPP was 1:1, the temperature, oxygen supply, and dissolved organic carbon degradation were improved. The NH₃, N₂O, and CH₄ emissions were reduced by 32.2, 18.3, and 90.7% compared with a treatment with RPP as a unique bulking agent. The RPP had no effect on conserving nitrogen during sludge composting; the total nitrogen loss was reduced from 29.3 to 18.2% when sawdust was mixed with RPP in a ratio of 1:1. Therefore, mixing RPP and sawdust in the dry weight ratio of 1:1 (sawdust: RPP) can be potentially used for reducing composting cost and improving the sewage sludge composting by reducing the amount of sawdust mixed and mitigating GHG and NH₃ emissions.

Metagenomic analysis revealed the microbiota and metabolic function during co-composting of food waste and residual sludge for nitrogen and phosphorus transformation

This paper used bagasse as a composting additive and bulking agent in order to investigate the aerobic composting process of food waste and residual sludge. Accordingly, the variations of nitrogen and phosphorus nutrients, microbiota and metabolic function during the composting process were systematically explored. Three piles with residual sludge, food waste and bagasse mass ratios of 1:1:1, 2:1:1 and 4:1:1 were set. The ammonia nitrogen content in the three compost piles were 3.18 mg/g, 4.68 mg/g and 5.84 mg/g at the end of composting. The final available phosphorus content of the three piles were 3.42 mg/g, 6.70 mg/g and 11.21 mg/g, respectively. X-ray photoelectron spectroscopy (XPS) analysis showed that absorption peaks attributed to amines, amino acids and amides appeared in the 1:1:1 pile. Metagenomic analysis of the glycolysis and ammonia transformation pathways showed that the total relative abundance of key enzyme genes for the conversion of glucose to glucose-6-phosphate in the three plies were 0.326%, 0.213% and 0.248%, respectively. The total relative abundance of 2 glutamate dehydrogenase (GDH2), glud1-2 and E1,4,1,4 dehydrogenases in the three piles was 0.125%, 0.151% and 0.160%, respectively, as the main enzymes for the mutual conversion of ammonia and glutamate.

Microbial degradation in the co-composting of pig manure and biogas residue using a recyclable cement-based synthetic amendment

This research investigated a synthetic amendment to improve composting and resource recycling of pig manure and biogas residue. We further examined whether adding a synthetic amendment impacts the microbial ecosystem in the composted materials. Three mixing ratios were used to investigate composting performance: no synthetic amendment (T0), 5% synthetic amendment (T1), and 10% synthetic amendment (T2) (T1 and T2 were measured as a wet weight ratio). There were no significant differences in the fundamental characteristics between composting products in T0 and T1. The moisture content of composting material in T0, T1, and T2 significantly decreased from a baseline of approximately 65% to 35.5%, 37.3%, and 55.9%, respectively. Meanwhile, the germination index significantly increased to 111.6%, 155.6%, and 62.3%, respectively. When an optimal proportion of synthetic amendment was added, T1 showed high degree of humification, lignocellulase activities, and effective biodegradation. Firmicutes, Actinobacteria, Proteobacteria, and Bacteroidetes were the dominant bacteria, while Ascomycota and Basidiomycota were the dominant fungi in all treatment groups. Amino sugar and nucleotide sugar metabolism, glycolysis, starch, and sucrose metabolism were among the primary pathways in predicted functions. The synthetic amendment can generate a mature composting product and can be reused or recycled to conserve resources.

The physical structure of compost and C and N utilization during composting and mushroom growth in Agaricus bisporus cultivation with rice, wheat, and reed straw-based composts

The cultivation of Agaricus bisporus with compost made from wheat (Triticum aestivum L.), rice (Oryza sativa L.), and reed (Phragmites australis Trin.) straw was investigated. Straw degradation was analyzed at the microscopic level, and the corresponding changes in the breakdown of different lignocellulose components during different phases of composting and mushroom production helped in understanding the yield-limiting factors of using different straws to grow mushrooms. The wheat straw compost resulted in the highest mushroom production and had the highest bioconversion efficiency. The rice straw was limited by the softer texture, which resulted in low-porosity and overdecomposed compost in the composting process and decreased the amount of available lignocellulose during mycelial growth. Although reed straw had the largest carbon resources, its utilization rate was the lowest. The hard structure, low water holding capacity, and high porosity increased the recalcitrance of reed straw to degradation and prolonged the composting time, which resulted in large N and C losses and an increased C/N ratio. Moreover, reed straw failed to transform into "ready-to-consume C" in composting. Therefore, a high C/N ratio and deficiency of available nutrition decreased the utilization efficiency of the lignocellulosic components by A. bisporus during mycelial colonization and mushroom production. The investigation revealed that degradability by and availability to microbiota and A. bisporus seemed to be the overriding factors for optimizing the composting process with different straw types. KEY POINTS: • The physical structure of compost has a significant influence on the composting process. • Degradability and availability are key factors in compost quality evaluation. • Lignocellulose utilization efficiency positively correlated with mushroom yield.

Microbial succession and degradation during kitchen waste biodrying, highlighting the thermophilic phase

Biodrying in conjunction with compound stone amendment was used to treat kitchen waste, which improved biodrying. After 16 days, the pile moisture content decreased from 68.8% to 23.0%. Lignin, cellulose and hemicellulose concentrations decreased from 104.6 mg g^-1 d.b., 322.9 mg g^-1 d.b. and 155.9 mg g^-1 d.b., respectively, to 74.0 mg g^-1 d.b., 224.8 mg g^-1 d.b. and 134.5 mg g^-1 d.b., respectively. The Shannon index for bacteria increased from 2.5 to 3.1, while for fungi, it decreased from 4.6 to 0.6. The relative abundances of Amino Acid Metabolism and Carbohydrate Metabolism exceeded 7%. The thermophilic phase during the process inactivated the pathogenic microorganisms, increased the bacterial diversity, decreased the fungal diversity, and potentially improved the metabolism of nutrients, including amino acids, carbohydrates, lipids and vitamins. The biomarker analysis and predicated protein sequences provide genetic evidence to elucidate why the thermophilic phase is the peak time for nutrient metabolism.

Advanced treatment of dye wastewater using a novel integrative Fenton-like/MnO2-filled upward flow biological filter bed system equipped with modified ceramsite

The deposal of residual hydrogen peroxide (H₂O₂) in Fenton-like system and the requirement of oxygen in bioreactor are essential parts for the treatment of integrative Fenton-like/bioreactor. A novel low-cost integrative Fenton-like and MnO₂-filled upward flow biological filter bed (Fenton-like/MBFB) equipped with the modified ceramsite was constructed to evaluate the main properties and catalytic activity of modified ceramsite, and the optimal conditions of integrative system and compare integrative and traditional systems. In this study, the Fenton-like reactor with modified ceramsite had higher catalytic ability whose Acid Orange 7 (AO7) degradation efficiency reached to 79.3% due to large surface area and high porosity, compared with that with raw ceramsite (44.3%). Furthermore, total utilization efficiency of H₂O₂ in integrative system (from 32.41% to 53.51%) and removal efficiencies of COD and AO7 were remarkably improved, which would effectively decrease the waste of H₂O₂ and the setting of regulation pool and aeration tank. Thus, the integrative system can save 0.51 CNY/m³ in construction cost and 0.21 CNY/m³ in operating cost. The average COD removal efficiency, AO7 degradation efficiency and effluent DO concentration were achieved to 64.8%, 79.5% and 9.3 mg/L respectively in integrative system were achieved in integrative system during sixty successive runs. Also, the potential degradation pathway of contaminants was also proposed according to the OH-enhanced at Fenton-like reactor due to catalyst and adsorption of modified ceramsite and the removal of microorganisms and modified ceramsite for contaminants at MBFB. This study demonstrated the feasibility of integrative Fenton-like/MBFB filled with modified ceramsite for simultaneously decreasing operational cost and complexity and enhancing removal efficiency, thus provided a one-step alternative for refractory dye wastewater.

Adding a recyclable amendment to facilitate sewage sludge biodrying and reduce costs

Finding an economical amendment, available in a steady supply, is needed to support the biodrying industrialization. This research developed a recyclable biodrying amendment (RBA) to condition the biodrying of sewage sludge. The pilot-scale treatment (T_R), which included the addition of equivalent weights of RBA and sawdust as amendments, resulted in a higher pile temperature and longer thermophilic phase compared to the control (T_C), which used only sawdust as an amendment. The final moisture content levels were below 50% with both T_R and T_C. The heat use efficiency for water evaporation was 72.2% and 73.0% in T_R and T_C, respectively. The activity of α-amylase and cellulose 1,4-β-cellobiosidase increased during the thermophilic phase, while the activity of endo-1,4-β-glucanase and endo-1,4-β-xylanase decreased during the thermophilic phase with both T_R and T_C. The fourier-transform infrared spectra indicated that adding the RBA resulted in good biodegradability of the lipids, proteins, and polysaccharides. The humic acid to fulvic acid ratio in T_R and T_C increased from 0.33 (T_R) and 0.35 (T_C) on day 0-0.46 (T_R) and 0.45 (T_C) on day 21, indicating the humification process. The RBA recovery rate was 95.6% and can be reused. These findings highlight that adding RBA showed satisfactory biodrying performance, reduced the amendment cost, and the biodrying product could be incinerated without energy deficit.

Using the modified pine wood as a novel recyclable bulking agent for sewage sludge composting: Effect on nitrogen conversion and microbial community structures

This study investigated the effect of a recoverable sulphuric acid and sodium hydroxide-modified pinewood (MOP) as a bulking agent during sewage sludge and sawdust composting (MOPC), with a control experiment using unpretreated pinewood (UNP; UNPC) as the bulking agent. Results show that addition of MOP effectively promoted the degradation of organic matter during composting. The maximum temperature increased by 1.50 °C and the high temperature period (T > 50 °C) of composting was extended 4 days longer than the control experiment. Furthermore, MOP addition reduced the loss of nitrogen by 9.40%. High-throughput sequencing analysis showed that the bacterial communities in the UNPC and MOPC treatments were significantly different. Pseudoxanthomonas was the dominant bacteria during the thermophilic and cooling phases of the MOPC treatment. In addition, the recycling efficiency of the UNP and MOP was 99.18% and 99.37%, respectively.

Passivation of lead and cadmium and increase of the nutrient content during sewage sludge composting by phosphate amendments

As an efficient and cost-effective biological treatment method for sewage sludge, composting has been widely used worldwide. To passivate heavy metals and enhance the nutrient content in compost, in the present study, phosphate rock, calcium magnesium phosphate, and monopotassium phosphate were added to the composting substrate. According to the Community Bureau of Reference sequential extraction procedure, phosphate rock and monopotassium phosphate amendments exhibit a good passivation effect on Cd and Pb. The X-ray diffraction patterns proved the formation of Pb₃(PO₄)₂ and Cd₅(PO₄)₂SiO₄ crystals, and X-ray absorption near-edge structure spectroscopy illustrated the change in P speciation after phosphate amendment. Furthermore, phosphate amendment increased the contents of total P and available P, and it reduced the loss of N during sewage sludge composting. The germination index showed that the target phosphate amendments in sewage sludge compost had no negative effects on seed germination, and this method has great potential to be used as a soil amendment.

Perlite as the partial substitute for organic bulking agent during sewage sludge composting

Composting is an efficient and cost-effective technology for sewage sludge treatment, and bulking agents are essential in sewage sludge composting. In this study, perlite was chosen as inorganic bulking agent to partially substitute for the organic bulking agent. Variations in the temperature, bulk density, moisture content, pH, electrical conductivity, organic carbon, nitrogen, phosphorus and potassium were detected during sewage sludge composting. The treatment with a mass ratio of spent mushroom substrate to perlite at 3:1 exhibited the highest pile temperature and the best effect on reducing bulk density and moisture content. In addition, Fourier transform infrared spectra showed that perlite promotes the degradation of organic matter during the composting process, and the germination index showed that the compost from all treatments was safe for agricultural application. When the mass ratios of spent mushroom substrate and perlite at 3:1 and 2:2 were chosen as bulking agents, the sewage sludge compost product could be used to produce plant cultivation substrate, and economic benefits could be obtained from sewage sludge composting according to comprehensive cost analysis.

Preservation of nitrogen and sulfur and passivation of heavy metals during sewage sludge composting with KH2PO4 and FeSO4

Composting is an effective method for treating sewage sludge. The aim of this work was to study preservation of nitrogen and sulfur and passivation of heavy metals during sewage sludge composting with KH₂PO₄ and FeSO₄. The results show the loss rate of N decreased by 27.5% while that of S was increased by 32.1% compared with the control treatment during composting when KH₂PO₄ and FeSO₄ were added. X-ray absorption near-edge structure spectra show that S was converted to a highly oxidizable state during sewage sludge composting with added KH₂PO₄. The mobility factors of Cu, Zn, and Pb after composting were found to decrease by 13.6%, 21.6%, and 3.8%, respectively, compared with those before composting when KH₂PO₄ was added. Adding these two materials to Cu and Zn inhibits Zn₃(PO₄)₂(H₂O)₄ and Cu₅(PO₄)₂(OH)₄ from transforming into more mobile forms, while adding these materials to Pb promotes Pb₃(PO₄)₂ formation.

Pilot-scale composting of typical multiple agricultural wastes: Parameter optimization and mechanisms

In this work, pilot-scale (100 kg of mixed wastes each time) composting of typical agricultural wastes, including chicken manure, vegetable leaves and rice husks with a mass ratio of 6:3:1, was studied. Effects of thermal phases and transformation time on performance, including moisture, nutrient, and carbon contents and C/N ratios of compost, were investigated. The optimal parameters were 75 ± 5 °C and 18 h; the compost met the requirements of Chinese National Agricultural Organic Fertilizer Standard (NY525-2012). Mechanisms investigations demonstrated that, Bacillus and Sinibacillus played key roles in degrading high-molecular-weighted organic substances into small-molecular-weighted humic- and fulvic-acid-like matters, resulting in smaller particle size and loose structure of the product; rice husk particles acted as a conditioning agent and remained their originally morphology. The mechanism provided informative guidance for optimizing the process in practical application.

Effect of phosphate amendments on improving the fertilizer efficiency and reducing the mobility of heavy metals during sewage sludge composting

Composting has been globally applied as an effective and cost-efficient process to manage and reuse sewage sludge. In the present study, four different phosphates as well as a mixture of ferrous sulfate and monopotassium phosphate were used in sewage sludge composting. The results showed that these phosphate amendments promoted an increase in temperature and the degradation of organic matter as well as reduction on nitrogen loss during 18 days of composting. In addition, ferrous sulfate and phosphate had a synergistic effect on reducing nitrogen loss. The contents of total phosphorus and available phosphorus in the compost with addition of 1% phosphate were 40.9% and 66.1% higher than the compost with control treatment. Using the BCR (Community Bureau of Reference) sequential extraction procedure, the addition of calcium magnesium phosphate significantly reduced the mobility factor of Cd, Zn and Cu by 24.2%, 1.7% and 18.8%, respectively. The mobility factors of Pb were increased in all samples, but the monopotassium phosphate treated sample exhibited the greatest Pb passivation ability with the lowest mobility factor increase (1.8%) among all treatments. The X-ray diffraction patterns of compost samples indicated that the passivation mechanism of Cu and Zn may be the forming CuFeS₂ and ZnCu(P₂O₇) crystals during sewage sludge composting. The germination index showed that the compost of all treatments was safe for agricultural application; the germination index of the calcium magnesium phosphate treatment was 99.9 ± 11.8%, which was the highest among all treatments.