Assessing the agricultural reuse of the digestate from microalgae anaerobic digestion and co-digestion with sewage sludge

Effect of pretreated and anaerobically digested microalgae on the chemical and biochemical properties of soil and wheat grown on fluvisol

In this study, the effects of the potential application of digestate as an agricultural fertiliser obtained from anaerobically digested microalgae treated by three pretreatment methods, namely alkaline hydrogen peroxide (AHP), high temperature and pressure (HTP), and hydrodynamic cavitation (HC) on some properties of soil, and wheat growth and yield were investigated. For this purpose, pretreated and anaerobically digested microalgae digestates alone or together with diammonium phosphate (DAP) as a chemical fertiliser were applied to soil for wheat growth. The highest dosage of AHP pretreated digestate combined with a half dose of DAP applied to soil was rich in nutrients as 0.25%N and 7.19 mg kg-1 compared to all groups. The properties of the soils were enhanced by applying the highest dosage (0.06 g kg-1) of microalgae digestate combined with a half dose of DAP. 0.02 g kg-1 dosage of HC pretreated digestate combined with a half dose of DAP also greatly improved nitrogen use efficiency indices by up to 104%. The soils' enzyme activities increased in wheat growth experiments by applying either raw or pretreated microalgae digestates. The soils' β-glycosidase, alkaline phosphatase, and urease enzyme activities increased to 1.38 mg pNP g-1 soil, 4.91 mg pNP g-1 soil, and 2.27 mg NH4-N 100 g-1 soil respectively by the application of highest dosage of HC pretreated digestate. The digestates did not have a toxic effect on wheat growth, it was determined that applied pretreatment processes did not cause significant changes in wheat plant height or wet and dry weight.

The effects of microalgae use as a biofertilizer on soil and plant before and after its anaerobic (co-)digestion with food waste

The increase in food waste generation has resulted in significant challenges for its sustainable management. Anaerobic digestion coupled with microalgae-based ponds for digestate treatment can be used as a low-cost eco-friendly technology approach. In this case, microalgal biomass harvested from the ponds may be valorized into bioenergy (biogas) and soil conditioner and/or biofertilizers. The aim of the present study was to evaluate the microalgal biomass produced from a food waste digestate treatment ponds as agricultural fertilizer. For this purpose, microalgal biomass was tested before and after anaerobic digestion and co-digestion with food waste, exploring its potential for valorization. The inorganic fertilizer urea and soil with no fertilization were also used as treatments. The experimental design consisted of applying the treatments in pots cultivated with hybrid grass Brachiaria cv. Sabiá and distributed in randomized blocks in a controlled greenhouse. Microalgal biomass was mainly composed by Scenedesmus sp.. The assessed parameters showed comparable results on plant growth (i.e. number of tillers, fresh and dry matter and Chlorophyll content index) for fresh and digested microalgal biomass and inorganic fertilizer. Furthermore, it was observed that fresh microalgae provided the highest Phosphorus content in the leaf (21 %). Additionally, there were increases of 9 % in Nitrogen and 12 % in organic matter in the soil after applying digested microalgae compared to the control group without any fertilization. Finally, experimental data obtained suggests that microalgae-based biofertilizer holds the potential to replace inorganic fertilizer as a nutrient source. Moreover, it contributes to the valorization of by-products from organic waste treatment.

Assessing sustainability of microalgae-based wastewater treatment: Environmental considerations and impacts on human health

An integrated life cycle assessment (LCA) and quantitative microbial risk assessment (QMRA) were conducted to assess microalgae-mediated wastewater disinfection (M-WWD). M-WWD was achieved by replacing ultraviolet disinfection with a microalgal open raceway pond in an existing sewage treatment plant (STP) in India. Regarding impacts on human health, both M-WWD and STP yielded comparable life cycle impacts, around 0.01 disability-adjusted life years (DALYs) per person per year. However, QMRA impacts for M-WWD (0.053 DALYs per person per year) were slightly lower than that for STP while considering exposure to E. coli O157:H7 and adenovirus. Additionally, a comparative LCA resolved the dilemma about the appropriate utilization of microalgal biomass. Among biodiesel, biocrude, and biogas production, the lowest impacts of 0.015 DALYs per person per year were obtained for biocrude for 1 m3 water treated by M-WWD. Electricity consumption in microalgae cultivation was a major environmental hotspot. Overall, M-WWD, followed by production of microalgal biocrude, emerged as a sustainable alternative from environmental and public health perspectives. These findings set the foundation for pilot-scale M-WWD system development, testing, and economic evaluation. Such comprehensive investigations, encompassing LCA, QMRA, and resource recovery scenarios, offer crucial insights for stakeholders and decision-makers in wastewater treatment and environmental management.

Feasibility of anaerobic co-digestion of biodegradable plastics with food waste, investigation of microbial diversity and digestate phytotoxicity

The effects of biodegradable plastics of different thicknesses (30 and 40 μm) and sizes (20 × 20, 2 × 2, and 1 × 1 mm) on anaerobic digestion of food waste and digestate phytotoxicity were investigated. Methane productions (38 days) for the groups with 20 × 20, 2 × 2, and 1 × 1 mm of 30 μm plastics were 92.46, 138.27, and 259.95 mL/gVSremoval, respectively which are nearly 58 % higher than the control group (58.86 mL/gVSremoval). Methane production in 40 μm plastics groups was lower than in 30 μm groups of equal size. All sizes of 30 µm plastics promoted substrate hydrolysis, acidification, and relative abundance of key hydrolytic bacteria and methanogens. Phytotoxicity tests results showed that seed root elongation was inhibited in groups with 40 μm plastics. In conclusion, 30 μm biodegradable plastics were more suitable for anaerobic digestion with food waste than 40 μm.

Strategies of managing solid waste and energy recovery for a developing country - A review

Solid waste is considered one of the major pollutants of both water and surface worldwide. The growing global population, urban expansion, and industrial growth are the main reasons for solid waste generation. This has become a major challenge with both regional and worldwide consequences. The yearly generation of municipal solid wastes around the world is 2.01 BT (billion tons) among which about 33 % are not ecologically handled. To address this, proper solid waste management, especially recycling waste products, is crucial to achieving sustainability. High-income countries are able to recycle 51 % of their waste, while low-income countries only recycle 16 % of their waste. Inadequate solid waste management practices can only compound environmental and social problems. To handle these issues thermochemical and biochemical methods are used to convert solid waste to energy. Thermochemical method is suitable for developing countries though it is energy extensive. This review provides a detailed analysis of developing countries' solid waste management and energy recovery. It explores energy recovery technologies, including thermochemical and biochemical waste conversion processes.

Life cycle assessment of microalgae systems for wastewater treatment and bioproducts recovery: Natural pigments, biofertilizer and biogas

The aim of this study was to assess the potential environmental impacts associated with microalgae systems for wastewater treatment and bioproducts recovery. In this sense, a Life Cycle Assessment was carried out evaluating two systems treating i) urban wastewater and ii) industrial wastewater (from a food industry), with the recovery of bioproducts (i.e. natural pigments and biofertilizer) and bioenergy (i.e. biogas). Additionally, both alternatives were compared to iii) a conventional system using a standard growth medium for microalgae cultivation in order to show the potential benefits of using wastewater compared to typical cultivation approaches. The results indicated that the system treating industrial wastewater with unialgal culture had lower environmental impacts than the system treating urban wastewater with mixed cultures. Bioproducts recovery from microalgae wastewater treatment systems can reduce the environmental impacts up to 5 times compared to a conventional system using a standard growth medium. This was mainly due to the lower chemicals consumption for microalgae cultivation. Food-industry effluent showed to be the most promising scenario for bioproducts recovery from microalgae treating wastewater, because of its better quality compared to urban wastewater which also allows the cultivation of a single microalgae species. In conclusion, microalgae wastewater treatment systems are a promising solution not only for wastewater treatment but also to boost the circular bioeconomy in the water sector through microalgae-based product recovery.

The advantages of co-digestion of vegetable oil industry by-products and sewage sludge: Biogas production potential, kinetic analysis and digestate valorisation

The production of edible vegetable oils generates considerable amounts of energy-rich waste, which is usually not utilised fully. Besides, inefficient management of such wastes can have a negative impact on the environment. On the other hand, this waste can also serve as a raw material for the production of high value-added products, such is biogas. The mono-digestion of seven different by-products and wastes from the vegetable oil industry was investigated in this study: Pumpkin seeds press cake (PSPC), grape seeds press cake (GSPC), olive mill pomace (OMP), coconut oil cake (CC), filtration additive (FA), spent bleaching earth (SBE) and sludge from a vegetable oil industry (SOI) wastewater treatment plant. In addition, co-digestion of these substrates was performed with municipal sewage sludge (SS). Besides inoculum, rumen fluid was added to the reactors to enhance biogas production. The biogas production potential of the tested substrates was monitored by measuring various parameters. A kinetic analysis was later carried out and a growth test was performed on the digestates to evaluate their potential for agricultural use. The highest biogas yields in the mono-digestion test were obtained with the substrates with the highest fat content: 1402, 1288, 830 and 750 mL of biogas/gVS for SOI, FA, PSPC and CC substrate, respectively. Co-digestion of SS with by-products of vegetable oil industry such as FA, SBE, CC, SOI and PSPC increased the biogas yields by 94.9%, 74.1%, 30.8%, 27.4% and 23.6% compared to SS mono-digestion. Furthermore, the data for mono-digestion of PSPC, GSPC, and FA, and co-digestion of SS with these substrates, CC and SBE, have not been found in the literature to date. The maximum methane content ranged from 61 to 74 vol%, while the chemical oxygen demand removal efficiency ranged from 42 to 78%. Relatively high fatty acids contents and ammonium concentrations were measured in the reactors. Kinetic analysis showed the best fit to the experimental data for the Cone kinetic model (R² > 0.98). The First order kinetic model, Monod, and the modified Gompertz model also exhibited high R² values. The digestates obtained from co-digestion proved to be excellent in the cress seeds growth test at digestate concentrations of 5-10 wt%, while higher concentrations had a toxic effect.

Sustainable microalgal biomass valorization to bioenergy: Key challenges and future perspectives

The global trend is shifting toward circular economy systems. It is a sustainable environmental approach that sustains economic growth from the use of resources while minimizing environmental impacts. The multiple industrial use of microalgal biomass has received great attention due to its high content of essential nutrients and elements. Nevertheless, low biomass productivity, unbalanced carbon to nitrogen (C/N) ratio, resistant cellular constituents, and the high cost of microalgal harvesting represent the major obstacles for valorization of algal biomass. In recent years, microalgae biomass has been a candidate as a potential feedstock for different bioenergy generation processes with simultaneous treating wastewater and CO₂ capture. An overview of the appealing features and needed advancements is urgently essential for microalgae-derived bioenergy generation. The present review provides a timely outlook and evaluation of biomethane production from microalgal biomass and related challenges. Moreover, the biogas recovery potential from microalgal biomass through different pretreatments and synergistic anaerobic co-digestion (AcoD) with other biowastes are evaluated. In addition, the removal of micropollutants and heavy metals by microalgal cells via adsorption and bioaccumulation in their biomass is discussed. Herein, a comprehensive review is presented about a successive high-throughput for anaerobic digestion (AD) of the microalgal biomass in order to achieve for sustainable energy source. Lastly, the valorization of the digestate from AD of microalgae for agricultural reuse is highlighted.

The influence of bio-plastics for food packaging on combined anaerobic digestion and composting treatment of organic municipal waste

The use of bio-plastic-based packaging as an alternative to conventional plastic packaging is increasing. Among the plethora of different bio-based plastics, the most relevant ones are those that, at the end of their life, can be treated with the organic fraction of municipal solid waste. Even in these cases, their impact on the waste processing and recycling is not always positive. This study aim to assess on a laboratory scale the influence on combined anaerobic digestion and composting industrial processes of a bio-based plastic film, namely cellulose acetate (CA), in pure and modified (additions of additive) forms. CA films were mixed with organic waste and subjected to: (i) anaerobic digestion; (ii) active composting and (iii) two stages of curing composting. Anaerobic digestion and composting were monitored through methane yield and oxygen uptake respectively; additionally, the bio-plastics degree of disintegration was assessed during all the processes. The final disintegration of pure and modified CA was 73.82% and 54.66%, respectively. Anaerobic digestion contributes to the disintegration of the material, while aerobic treatment appears to be nearly ineffective, especially for modified CA. The presence of cellulose acetate during anaerobic digestion of food waste increased the methane yield by about 4.5%. Bioassay confirmed the absence of possible toxic effects on the final compost from the bio-plastic treatment. Although bio-based materials are not the only solution to plastic pollution, the findings confirm the need to upgrade the organic waste treatment plants and the necessity to revise the requirements for the use of compost in agriculture.

Microalgae based wastewater treatment coupled to the production of high value agricultural products: Current needs and challenges

One of the main social and economic challenges of the 21st century will be to overcome the worlds' water deficit expected by the end of this decade. Microalgae based wastewater treatment has been suggested as a strategy to recover nutrients from wastewater while simultaneously producing clean water. Consortia of microalgae and bacteria are responsible for recovering nutrients from wastewater. A better understanding of how environmental and operational conditions affect the composition of the microalgae-bacteria consortia would allow to maximise nutrient recoveries and biomass productivities. Most of the studies reported to date showed promising results, although up-scaling of these processes to reactors larger than 100 m² is needed to better predict their industrial relevance. The main advantage of microalgae based wastewater treatment is that valuable biomass with unlimited applications is produced as a co-product. The aim of the current paper was to review microalgae based wastewater treatment processes focusing on strategies that allow increasing both biomass productivities and nutrient recoveries. Moreover, the benefits of microalgae based agricultural products were also discussed.

Water resource recovery coupling microalgae wastewater treatment and sludge co-digestion for bio-wastes valorisation at industrial pilot-scale

This case study is part of a circular bioeconomy project for a winery company aiming to integrate a microalgae-based system within the existing facilities of the winery WWTP, promoting nutrient recovery and transformation into valuable products and bioenergy. Microalgae were used for wastewater treatment, removing N-NH₄⁺ (97%) and P-PO₄^-3 (93%). A pilot anaerobic reactor was used for batch anaerobic mono-digestion of secondary sludge (WAS) and for co-digestion of WAS and algal biomass. The methane yield using WAS from two different wine production seasons was 155.4 and 132.9 NL CH₄ kg VS^-1. Co-digestion led to the highest methane yield (225.8 NL CH₄ kg VS^-1). The application of the bio-wastes for fertilization was assessed through plant growth bioassays: mono- and co-digestion digestates and dry algal biomass enhanced plant biomass accumulation (growth indexes of 163%, 155% and 121% relative to those of the control - commercial amendment, respectively), demonstrating a lack of phytotoxicity.

Biologia Futura: potential of different forms of microalgae for soil improvement

Products derived from microalgae have great potential in diverse field. As a part of the enhancing agriculture application, various forms of microalgae applications have been developed so far. They are known to influence soil properties. The various forms of application may enhance soil in more or less similar manner. They can help improve soil health, nitrogen, and phosphorus content, and even carbon sequestration. Thus, overall, it can enhance fertility of the soil.

Industrial symbiosis of anaerobic digestion and pyrolysis: Performances and agricultural interest of coupling biochar and liquid digestate

The sustainability of the anaerobic digestion industry is closely related to proper digestate disposal. In this study, an innovative cascading biorefinery concept coupling anaerobic digestion and subsequent pyrolysis of the digestate was investigated with the aim of enhancing the energy recovery and improving the fertilizers from organic wastes. Continuous anaerobic co-digestion of quinoa residues with wastewater sludge (45/55% VS) exhibited good stability and a methane production of 219 NL CH₄/kg VS. Subsequent pyrolysis of the solid digestate was carried out (at 500 °C, 1 h, and 10 °C/min), resulting in a products distribution of 40 wt% biochar, 36 wt% bio-oil, and 24 wt% syngas. The organic phase (OP) of bio-oil and syngas exhibited higher and lower heating values of 34 MJ/kg and 11.8 MJ/Nm³, respectively. The potential synergy of coupling biochar with liquid digestate (LD) for agronomic purposes was investigated. Interestingly, coupling LD (at 170 kg N/ha) with biochar (at 25 tons/ha) improved the growth of tomato plants up to 25% compared to LD application alone. In parallel, co-application of biochar with LD significantly increased the ammonia volatilization (by 64%) compared to LD application alone, although their simultaneous use did not impact the C and N mineralization rates.

Benefits and risks of agricultural reuse of digestates from plastic tubular digesters in Colombia

The aim of this study is to characterize the digestates from three plastic tubular digesters implemented in Colombia fed with: i) cattle manure; ii) cattle manure mixed with cheese whey; iii) pig manure. All the digesters worked under psychrophilic conditions. Physico-chemical characteristics, heavy metals, pathogens, and agronomic quality were investigated. All the digestates were characterized by physico-chemical characteristics and nutrients concentration suitable for their reuse as biofertilizer. However, these digestates may only partially replace a mineral fertilizer due to the high nutrients dilution. Heavy metals were under the detection limit of the analytical method (Pb, Hg, Ni, Mo, Cd, Chromium VI) or present at low concentration (Cu, Zn, As, Se) in all the digestates. Biodegradable organic matter and pathogens (coliform, helminths and Salmonella spp.) analysis proved that all the digestates should be post-treated before soil application in order to prevent environmental and health risks, and also to reduce residual phytotoxicity effects. The digestate from pig manure had a higher nutrient percentage (0.2, 0.6 and 0.05 % w/w of total N, P₂O₅ and K₂O, respectively), but also higher residual phytotoxicity than the other digestates. Co-digestion seemed not to significantly improve the digestate fertilizing potential. Finally, further studies should address how to improve fertilizing potential of digestates from plastic tubular digesters, avoiding environmental and health risks.

The Effects of Soil Application of Digestate Enriched with P, K, Mg and B on Yield and Processing Value of Sugar Beets

The aim of this research was to find out if the supplementation of digestate, a by-product of the anaerobic digestion of sugar beet pulp, with phosphorus, potassium, magnesium and boron can improve digestate performance as a soil amendment. The materials of this study were: digestate and sugar beet roots (Beta vulgaris cv. Fighter). A field trial was carried out on sugar beet growth under soil application conditions of solid and liquid digestate fractions with or without supplementation with P, K, Mg and B. It was shown that the root yield obtained from the plots amended with digestate supplemented with P, K, Mg and B was higher compared to the yield of other treatments. Soil amendment with digestate supplemented with P, K, Mg and B affected quality parameters of sugar beet roots. An increase in the following parameters under the effects of enriched digestate application was found: sucrose content, dry residue, pomace content, inverted sugars, α-amino and amide nitrogen fractions, as well as sodium and potassium content. A reduction in the content of conductometric ash was noted but this difference was not proven. The enrichment of digestate with P, K, Mg and B resulted in the beneficial modification of beet roots’ processing parameters with the exception of the predicted content of sugar in molasses. In the case of the liquid fraction and its supplementation with P, K, Mg and B, six among eleven technological quality parameters were increased.

Reuse of the digestate obtained from the biomethanization of olive mill solid waste (OMSW) as soil amendment or fertilizer for the cultivation of forage grass (Lolium rigidum var. Wimmera)

The principal by-product from the two-phase olive oil production process is olive mill solid waste (OMSW). It is a highly-pollutant by-product, not only because of its characteristics, but also because of the considerable volume of OMSW which is generated, amounting to 2 to 4 million tons per year in Spain. The anaerobic digestion of this by-product is a well-studied process, and results in the generation of biogas, methane and carbon dioxide mainly of high calorific values (20-25 MJ m^-3), and an effluent or digestate. The digestate of this by-product has never been characterized. This study presents an informative view on how the composition of OMSW digestate shows promising implications as a soil amendment or fertilizer due to the quality of the biomass from Lolium rigidum, a useful grass specie for the production of forage. Three OMSW digestate alternative applications or treatments were investigated: the digestate and the solid fraction of the digestate for a nutrient-poor soil amendment and the liquid fraction of the digestate as fertilizer. The results confirm that all the OMSW digestate treatments studied presented suitable characteristics for agricultural use, and showed an optimal Carbon/Nitrogen ratio with adequate values for heavy metals which are below the limits established by the Spanish and European legislation in the absence of pathogens. However, fertirrigation was the treatment that provided Lolium rigidum with the best characteristics, improving its shoot biomass, photosynthetic rate and nutritional content.

Degradation of bioplastics in organic waste by mesophilic anaerobic digestion, composting and soil incubation

The aim of the study was to assess the effects of high concentrations (10 % w/w, data projected for 2030) of commercial bioplastics, i.e. starch based shopping bags (SBSB) and polylactic acid (PLA) tableware, in the organic fraction of municipal solid wastes (MSW) on compost quality obtained by pilot-scale dry mesophilic anaerobic digestion and subsequent composting of the digestate. After the biological processes, 48.1 % total solids (TS) of SBSB and 15 % TS of PLA degraded, resulting in a high bioplastics content (about 18 % TS) in compost. Subsequent compost incubation in soils indicated that bioplastics degraded by pseudo-zero order kinetics (0.014 and 0.010 mg C cm^-2 d^-1 for SBSB and PLA, respectively), i.e. complete degradation was expected in 1.6 years (SBSB) and 7.2 years (PLA), confirming the intrinsic biodegradability of bioplastics. Nevertheless, enhancing the rate and amount of bioplastics degradation during waste management represents a goal to decrease the amount of bioplastics reaching the environment.

Anaerobic digestion and agronomic applications of microalgae for its sustainable valorization

Microalgae are considered potential candidates in biorefinery processes, and due to their biochemical properties, they can be used in the production of biofuels such as biogas, as well as for bioremediation of liquid effluents. The objective of this review is to study the current status of microalgae anaerobic digestion and agricultural uses (as bio-stimulants and biofertilizers), starting from microalgae cultivation. Indeed, the efficiency of these processes necessarily depends on the evaluation of different biotic and abiotic factors that affect the growth of microalgae. However, the adaptation and the optimization of process parameters on a large scale is also limited by energy and economic constraints. Moreover, the integration of biogas production processes with microalgae cultivation allows a nutrients and CO2 virtuous loop, thus promoting the sustainability of the process. Finally, this paper provides a general overview of biogas and biofertilizers production combination, as well as the related challenges and recommended future research perspectives to complement the gap in the literature.

Circular economy fertilization: Phycoremediated algal biomass as biofertilizers for sustainable crop production

There is an urgent need to meet the demand of water and nutrients by their reuse and recycling to gratify sustainable food production system and resource conservation. Chlorella minutissima was found to be very effective in the removal of electrical conductivity (EC), total dissolved solids, phosphorous (P), potassium (K), ammonium, nitrate, biological oxygen demand (BOD₅) and chemical oxygen demand (COD) of sewage wastewater. We tested the effects of phycoremediated algal biomass addition to soil in field plots of baby corn and spinach, on plant growth, yield and soil chemical properties. The application of 100% nitrogen (N) fertilizer by algal biomass lead to higher economic yield of spinach and baby corn than recommended dose of mineral fertilizers. The available N and P content in experimental plots applied with algae biomass as biofertilizers were significantly higher than other treatments. The soil enzymes, such as urease, nitrate reductase, and dehydrogenase were analysed during the cropping season of baby corn and spinach. The soil supplied with 100% N by algae biomass (C. minutissima) significantly (P < 0.05) increased the dehydrogenase activity in spinach grown soil. While the nitrate reductase activity in soil supplied with algal manure was maximum (0.13 mg NO₂-N produced g^-1 soil 24 h^-1) and significantly higher than other treatments in baby corn grown soil. This study revealed that phycoremediation coupled with biofertilizers production from algae biomass is a recycling and resource conservation exercise to reduce eutrophication, recycling of wastewater, recycling of plant nutrients and improvement of the soil quality in circular economy fertilization.

Pretreatments for enhanced biomethane production from buckwheat hull: Effects on organic matter degradation and process sustainability

Buckwheat manufacturing produce a large amount of lignocellulosic residue (buckwheat hull), which could be used as substrate in anaerobic digestion, even if hard lignocellulosic structure represents the main obstacle for its degradation. This study presents the results of a laboratory experiment conducted to evaluate the effects of different pretreatments on buckwheat hull anaerobic digestion. To achieve the aim, five pretreatments (alkaline, thermo-alkaline, microwave, ultrasonication and low temperature thermal pretreatment) were studied and the results were compared to non treated buckwheat hull. Cumulative biomethane yields significantly increased after alkaline and thermo-alkaline pretreatments (+61% and +122% with respect to non treated hull, respectively). These results were mainly related to organic matter solubilisation (+772% and +859% of soluble reducing sugars, respectively) and lignin, hemicellulose and cellulose degradation. Overall, process parameters behaviour and digestate quality were not affected by the pretreatments. Alkaline and thermo-alkaline pretreatments were evaluated for their energetic and economic affordability, showing that combination of thermal and alkaline pretreatments ensures significant advantages.

Biodegradation of hydrophobic pesticides by microalgae: Transformation products and impact on algae biochemical methane potential

Intensive and extensive use of pesticides has contributed to their wide distribution in soil, air, and water. Due to their detrimental effects on non-target organisms, different technologies have been considered for their removal. In this work, three hydrophobic pesticide active compounds, namely, chlorpyrifos, cypermethrin, and oxadiazon, were selected to study the potential for their removal from aqueous media by a microalgae consortium. An abiotic and a killed control (thermally inactivated dead microalgae biomass) were employed to clarify their removal pathways, and pesticide content was quantified in liquid and biomass phases for 7 days. At the final time, total degradation (biodegradation plus photodegradation) contributed to the removal of 55% of oxadiazon, 35% of chlorpyrifos, and 14% of cypermethrin. Furthermore, more than 60% of chlorpyrifos and cypermethrin were removed by sorption onto microalgae biomass. Overall, the three pesticides showed high removal from the liquid phase. O,O-diethyl thiophosphate was identified in the liquid phase as a transformation product of chlorpyrifos formed by microalgae degradation. Phycoremediation was coupled with anaerobic degradation of the microalgae biomass containing the retained pesticides by sorption through biochemical methane potential tests. Anaerobic digestion was not inhibited by the pesticides as verified by methane production yields. The removal efficiency of the pesticides in the digestate was as follows: chlorpyrifos > cypermethrin > oxadiazon. These results highlight the potential of low-cost algal-based systems for the treatment of wastewater or effluents from agrochemical industries. The integration of wastewater treatment with biogas production through anaerobic digestion is a biorefinery approach that facilitates the economic feasibility of the process.

Improving the biogas yield of manure: Effect of pretreatment on anaerobic digestion of the recalcitrant fraction of manure

Anaerobic digestion of animal manure show a maximum of ca. 50% conversion of volatile solids due to recalcitrance of lignin and crystalline cellulose under anaerobic conditions. The aim of this study is to evaluate different pretreatments on anaerobic digestion of manure fibers after anaerobic digestion. Physical, chemical, thermal, and thermal combined with alkaline pretreatments using sodium hydroxide were tested on manure fiber fraction separated out after anaerobic digestion of cow manure. The anaerobic digestion after pretreatment along with untreated controls were done in semi-continuous anaerobic bioreactors. All pretreatments showed positive effect and the highest increase in VS conversion (42.4%) and methane yield (ca. 127%) was found for 3% NaOH pretreated sample at 180 °C. Composition analysis showed that cellulose, hemicellulose and lignin in digested manure fibers were optimally reduced by 24.8, 29.1 and 9.5% respectively during pretreatment and 76.5% of cellulose and 84.9% of hemicellulose was converted to methane during AD.

Effect of coupling alkaline pretreatment and sewage sludge co-digestion on methane production and fertilizer potential of digestate

This study aims at investigating how organic waste co-digestion coupled with alkaline pretreatment can impact the methane production and agronomic value of produced digestates. For this purpose, sludge alone and mixed with olive pomace or macroalgal residues were subjected to anaerobic digestion with and without alkaline pretreatment. In addition, co-digestion of pretreated sludge with raw substrates was also carried out and compared to the whole mixture pretreatment. KOH pretreatment enhanced methane production by 39%, 15% and 49% from sludge, sludge mixed with olive pomace and sludge mixed with macroalgal residues, respectively. The digestates were characterised according to their physico-chemical and agronomic properties. They were then applied as biofertilizers for tomato growth during the first vegetative stage (28 days of culture). Concentrations in chlorophyll a and carotenoids in tomato plants, following sludge digestate addition, rose by 46% and 41% respectively. Sludge digestate enhanced tomato plant dry weight by 87%, while its nitrogen content increased by 90%. The impact of nitrogen and phosphorus contents in the digestate was strongest on tomato plant dry weight, thus explaining the efficiency of sludge digestate relative to other types of digestate. However, when methane production is considered, the combination of pre-treatment with co-digestion of macroalgal residues and sludge appears most beneficial for maximizing energy recovery and for biofertilizer generation.

Evolution of phytotoxicity during the active phase of co-composting of chicken manure, tobacco powder and mushroom substrate

This study systematically investigated the phytotoxicity of chicken manure co-composted with tobacco powder and mushroom substrate on seed germination during active phase of composting. All compost products met the sanitation requirements specified in the Chinese national standard; however, only the mushroom substrate compost satisfied the maturity standard. From day 28, the composting entered the end of active phase and the concentrations of K+, Zn2+, Na+, Cu2+ and Fe3+ decreased gradually. Redundancy analysis indicated that the germination index, catalase and peroxidase activities was positively correlated with K+, Zn2+, Na+, Cu2+, Fe3+ and NO3--N, and negatively correlated with NH4+-N, Mg2+ and Ca2+, among which the most significant ions were Fe3+, Mg2+ and Zn2+ for all treatments. The malondialdehyde concentration of germinated seeds had adverse correlation with the above ions parameters.

Linking nitrous oxide emissions from starch wastewater digestate amended soil to the abundance and structure of denitrifier communities

Anaerobic digestion is widely used in starch wastewater pre-treatment and can remove the COD effectively, however, the effluents are nutritious and often need supplemental aerobic treatments to remove nutrients prior to discharge. The objective of this study was to investigate the feasibility of using the liquid digestate of starch wastewater (LDSW) as a fertilizer. This pot experiment was conducted with Ipomoea aquatica Forsk in a greenhouse with six treatment groups. The crop growth was significantly promoted, while the accumulation of soil nitrate was not influenced after LDSW addition, compared to the control. In addition, at the same nitrogen input, the yield of high-LDSW treatment was 65.2%, 92.3% and 69.2% higher than those of chemical fertilizer treatment during the three growth periods. Furthermore, average N₂O emission with high-LDSW addition was 15.8 g N/(ha.d), accounting for 15.0% of which under high chemical fertilizer treatment, due to the significantly enhanced denitrification genes (nirK, nirS and nosZ) abundance. Besides, the changes of soil N₂O-reducing bacteria were performed by high-throughput sequencing of nosZ. Our findings suggested that LDSW had many opportunities for sustainable agriculture to guarantee high yields while reducing negative environmental impacts.

Production of Microalgal Slow-Release Fertilizer by Valorizing Liquid Agricultural Digestate: Growth Experiments with Tomatoes

Anaerobic Digestion (AD) is a process that is well-known and fast-developing in Europe. AD generates large amounts of digestate, especially in livestock-intensive areas. Digestate has potential environmental issues due to nutrients (such as nitrogen) lixiviation or volatilization. Using liquid digestate as a nutrient source for microalgae growth is considered beneficial because digestate could be valorized and upgraded by the production of an added value product. In this work, microalgal biomass produced using liquid digestate from an agricultural biogas plant was investigated as a slow-release fertilizer in tomatoes. Monoraphidium sp. was first cultivated at different dilutions (1:20, 1:30, 1:50), in indoor laboratory-scale trials. The optimum dilution factor was determined to be 1:50, with a specific growth rate of 0.13 d−1 and a complete nitrogen removal capacity in 25 days of culture. Then, outdoor experiments were conducted in a 110 dm3 vertical, closed photobioreactors (PBRs) in batch and semi-continuous mode with 1:50 diluted liquid digestate. During the batch mode, the microalgae were able to remove almost all NH4+ and 65 (±13) % of PO43−, while the microalgal growth rate reached 0.25 d−1. After the batch mode, the cultures were switched to operate under semi-continuously conditions. The cell densities were maintained at 1.3 × 107 cells mL−1 and a biomass productivity around 38.3 mg TSS L−1 d−1 during three weeks was achieved, where after that it started to decline due to unfavorable weather conditions. Microalgae biomass was further tested as a fertilizer for tomatoes growth, enhancing by 32% plant growth in terms of dry biomass compared with the control trials (without fertilization). Similar performances were achieved in tomato growth using synthetic fertilizer or digestate. Finally, the leaching effect in soils columns without plant was tested and after 25 days, only 7% of N was leached when microalgae were used, against 50% in the case of synthetic fertilizer.

Evaluation of agronomic properties of digestate from macroalgal residues anaerobic digestion: Impact of pretreatment and co-digestion with waste activated sludge

The aim of this paper is to investigate the impact of pretreating macroalgal residue (MAR) from agar-agar extraction and its co-digestion with sewage sludge on methane production and the agronomic quality of the digestates produced. First, different pretreatments were assessed on BMP tests. Among milling technologies used, knife milling with a 4 mm-screen improved methane production by 25%. The MAR was then knife milled before alkaline, acid and thermal pretreatment. KOH pretreatment (5% TS basis, 25 °C for 2 days) led to the highest methane improvement. It was applied to semi-continuous anaerobic digestion and methane production achieved 237 Nml/gVS which was 20% higher than the control (198 Nml/gVS). In comparison to MAR mono-digestion, co-digestion with thickened activated sludge produced less methane (184 Nml/gVS) but reduced H₂S emission by 91%. None of the digestates was toxic for the germination or growth of wheat and tomato plants. Particularly, co-digestion had the highest impact on tomato plant dry weight (+94% compared to soil alone) mainly due to the phosphorous brought by sludge. However, the impact of alkaline pretreatment on plant growth was not significant.

Organic degrading bacteria and nitrifying bacteria stimulate the nutrient removal and biomass accumulation in microalgae-based system from piggery digestate

The microalgae-based system has been applied in anaerobic digestate treatment for nutrient removal and biomass production. To optimize its performance in treating piggery digestate, here, commercial bacterial agents, including organic degrading bacteria (Cb) and nitrifying bacteria (Nb), were inoculated into the microalgae-based system dominated by Desmodesmus sp. CHX1 (D). Reactor DN (inoculated with D and Nb) and DCN (inoculated with D, and Cb to Nb at a ratio of 1:2) have better performance on NH₄⁺-N removal, with a final efficiency at 40.26% and 39.87%, respectively, and no NO₃^--N or NO₂^--N accumulations. The final total chlorophyll concentration, an indicator of microalgal growth, reached 4.74 and 5.47 mg/L in DN and DCN, respectively, three times more than that in D. These results suggested that high NH₄⁺-N removal was achieved by the assimilation into high microalgal biomass after the inoculation with functional bacteria. High-throughput sequencing showed that the richness of microbial community decreased but the evenness increased by inoculating functional microorganisms. Microalgae aggregating bacteria were Cellvibrio, Sphingobacterium, Flavobacterium, Comamonas, Microbacterium, Dyadobacter, and Paenibacillus. This study revealed that the inoculation with functional bacteria reconstructed the microbial community which benefited for the microalgal growth and nutrient removal, providing a promising strategy for treating highly-concentrated digestate.

Pretreatment and co-digestion of microalgae, sludge and fat oil and grease (FOG) from microalgae-based wastewater treatment plants

The aim of this study was to assess the co-digestion of residual biomass flows generated in microalgae-based wastewater treatment plants: microalgae, primary sludge and fat, oil and grease (FOG), with and without microalgae thermal pretreatment. The results evidenced the high methane yield of FOG (563 mL CH₄/g VS) as compared to microalgae (140 mL CH₄/gVS) and sludge (299 mL CH₄/g VS). The methane yield of microalgae and sludge co-digestion (50-50% VS) was increased by 25 and 42% by adding 10 and 20% VS of FOG, respectively. Moreover, co-digestion trials improved the anaerobic digestion first-order kinetics by up to 67%. Regarding the thermal pretreatment, it increased the methane yield of microalgae by 60%, and 15% upon co-digestion with sludge and FOG. Therefore, co-digestion of microalgae, primary sludge and FOG appears as a promising strategy to enhance the biogas production, hence bioenergy recovery from wastewater, even without pretreatment.

Benefits and risks of long-term recycling of pharmaceutical sewage sludge on agricultural soil

European policy is direct towards increasing the agricultural reuse of sludge on soil for improving the fertility; however, the effects of long-term pharmaceutical sewage sludge (PSS) application on soil properties are still unknown. Thus, the aim of this work was to evaluate the agronomic and environmental effects on soil after 17 years of organic amendment with PSS derived from daptomycin production. Five different doses of PSS were spread on lands located in Anagni, Central Italy. Physico-chemical soil properties were investigated, as well as total and bioavailable heavy metals, changes in the soil organic matter quality and biochemical functioning. PSS application showed a positive agronomic potential, improving SOM quality, increasing soil humified organic matter and raising plant nutrients. SOM dynamic was different at low and high PSS supplies, as confirmed by the chemical and biochemical analysis (e.g. C biomass, FDA hydrolysis activity, basal respiration, dehydrogenase, urease and phosphatase activities). However, in a long-term agricultural reuse, environmental risks of PSS recycling were related to the increase of some heavy metals (Hg, Zn and Cu) and exchangeable Na.

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.

Strategic valorization of de-oiled microalgal biomass waste as biofertilizer for sustainable and improved agriculture of rice (Oryza sativa L.) crop

Intensive use of chemical fertilizer results in environmental pollution that disturbs the local ecosystem and causes reduction in the long-term crop yield. There is a need to explore the alternative source of plant nutrition such as de-oiled microalgal biomass as biofertilizer for sustainable production of food crops in a relatively pollution free environment. This study reports sustainable and improved agriculture of rice crop (cv. IR 36) by valorizing de-oiled microalgal biomass waste (DOMBW) of Scenedesmus sp., as eco-friendly fertilizer. The microalga (MA) was cultivated in open raceway pond using wastewater and flue gas. Performance evaluation and comparison of DOMBW with respect to growth and yield of rice plants vis-à-vis commercial chemical fertilizers (CF) and vermicompost (VC) applied individually or together, established the superiority of the former. The experiment comprised of five nutrient management treatments (CF₁₀₀, VC₁₀₀, MA₁₀₀, MA₅₀+CF_50, and MA₅₀+VC₅₀) meeting 100% nitrogen (N) recommendation either through a single source or combined application in the soil. Combining the application of microalgal based organic fertilizer with chemical fertilizer (MA₅₀+CF₅₀), showed the highest performance in terms of plant height, tiller number, biomass, and grain yield. At the harvest stage, MA₅₀+CF₅₀ also resulted in maximum plant dry weight, panicle weight, and 1000-grain weight in comparison to other treatments. This study revealed that the application of DOMBW as a biofertilizer is potentially sustainable and effective in improving the yields of rice crop with reduced use of chemical fertilizer.

Co-digestion of microalgae and primary sludge: Effect on biogas production and microcontaminants removal

Microalgal-based wastewater treatment plants are conceived as low cost and low energy consuming systems. The operation of these plants involves the management of primary sludge and microalgal biomass. The aim of this study is to analyse the anaerobic co-digestion of both by-products in terms of biogas production and contaminants of emerging concern removal. The co-digestion of microalgae and primary sludge (25/75% on a volatile solids basis) was investigated in continuous reactors and compared to microalgae mono-digestion at a hydraulic retention time of 20days. Results showed how the co-digestion enhanced the anaerobic digestion of microalgal biomass, since primary sludge is a more readily biodegradable substrate, which increased the methane production by 65% and reduced the risk of ammonia toxicity. Regarding the contaminants, musk fragrances (galaxolide and tonalide) and triclosan showed the highest abundance on primary sludge (0.5-25μg/g TS), whereas caffeine, methyl dihydrojasmonate and triphenyl phosphate were barely detected in both substrates (<0.1μg/g TS). The removal of these contaminants was compound-depending and ranged from no removal to up to 90%. On the whole, microalgae mono-digestion resulted in a higher removal of selected contaminants than the co-digestion with primary sludge.

Constructed wetlands for winery wastewater treatment: A comparative Life Cycle Assessment

A Life Cycle Assessment was carried out in order to assess the environmental performance of constructed wetland systems for winery wastewater treatment. In particular, six scenarios which included the most common winery wastewater treatment and management options in South-Western Europe, namely third-party management and activated sludge systems, were compared. Results showed that the constructed wetland scenarios were the most environmentally friendly alternatives, while the third-party management was the worst scenario followed by the activated sludge systems. Specifically, the potential environmental impacts of the constructed wetlands scenarios were 1.5-180 and 1-10 times lower compared to those generated by the third-party and activated sludge scenarios, respectively. Thus, under the considered circumstances, constructed wetlands showed to be an environmentally friendly technology which helps reducing environmental impacts associated with winery wastewater treatment by treating winery waste on-site with low energy and chemicals consumption.

First fertilizing-value typology of digestates: A decision-making tool for regulation

Defined as the residue from anaerobic digestion (AD), digestate refers to a set of materials with varied biochemical compositions. The objective of this study was to establish a digestate typology according to its fertilizing-value with data from literature and internal unpublished databases. To establish a relatively big database allowing the application of advanced statistics, usual fertilizing-value parameters were used: dry matter, volatile solids, C/N, C/Organic-N, total N (TN), total ammoniacal nitrogen (TAN), TAN/TN, total P and total K. Statistical analysis was performed on a dataset of 91 raw digestates, 34 solid fractions and 25 liquid fractions after separation. The resulting typology outlined that fertilizing-values are linked to AD feedstock and process. As case study regulations, no digestate (without any post-treatment) fulfilled French standards and the latest European Union regulation proposal on fertilizers. Options to reach regulations' product categories were discussed according to the typology. For the first time, a digestate typology was established based on fertilizing value, which can be a useful tool enhancing digestate management and policy making.

Effect of the mycotoxin aflatoxin B1 on a semi-continuous anaerobic digestion process

Cereals are primary crops and are the most important raw material for feed and food production. Increasing aflatoxin B1 (AFB1) contamination of corn is an emerging issue, and disposal procedures for AFB1-contaminated corn are not currently defined. Recovery of contaminated corn through anaerobic digestion may represent a suitable strategy for its valorisation; however, only a few studies concerning the effect of AFB1 on anaerobic processes can be found. Thus, the purpose of the present work was to evaluate the effect of the mycotoxin AFB1 on a semi-continuous anaerobic digestion (AD) process. Semi-continuous trials were carried out, and the biomethane production from ABF1-contaminated feedstocks (25, 50, and 100 µg kg^-1 AFB1 wet weight) was compared to that from non-contaminated feedstock. Moreover, the feasibility of the agronomic re-use of the digestate, and the fate of AFB1 during AD was assessed. No adverse effect of 25 µg kg^-1 AFB1 contamination of feedstock on biomethane yield was observed. In contrast, 100 µg kg^-1 AFB1 in the feedstock resulted in inhibition of the process due to the accumulation of organic acids, and to the decrease of the pH in the digestate (from 8.1 to 5.4). The continuous addition of AFB1-contaminated feedstock led to accumulation of the mycotoxin in the digestates. Consequently, a composting process should always precede the agricultural re-use of digestates in order to remove AFB1 and the residual phytotoxicity.

Start-up of a microalgae-based treatment system within the biorefinery concept: from wastewater to bioproducts

Within the European project INCOVER, an experimental microalgae-based treatment system has been built for wastewater reuse and added-value products generation. This article describes this new experimental plant and the start-up stage, starting from the new design of three semi-closed horizontal photobioreactors with low energy requirements for microalgae cultivation (30 m³ total), using agricultural runoff and urban wastewater as feedstock. The inflow nutrients concentration is adjusted to select cyanobacteria, microalgae able to accumulate polyhydroxybutyrates, which can be used for bioplastics production. Part of the harvested biomass is used as substrate for anaerobic co-digestion (AcoD) with secondary sludge to obtain biogas. This biogas is then cleaned in an absorption column to reach methane concentration up to 99%. The digestate from the AcoD is further processed in sludge wetlands for stabilization and biofertilizer production. On the other hand, treated water undergoes ultrafiltration and disinfection through a solar-driven process, then it is pumped through absorption materials to recover nutrients, and eventually applied in an agricultural field to grow energy crops by means of a smart irrigation system. This plant presents a sustainable approach for wastewater management, which can be seen as a resource recovery process more than a waste treatment.

Life cycle assessment of high rate algal ponds for wastewater treatment and resource recovery

The aim of this study was to assess the potential environmental impacts associated with high rate algal ponds (HRAP) systems for wastewater treatment and resource recovery in small communities. To this aim, a Life Cycle Assessment (LCA) was carried out evaluating two alternatives: i) a HRAP system for wastewater treatment where microalgal biomass is valorized for energy recovery (biogas production); ii) a HRAP system for wastewater treatment where microalgal biomass is reused for nutrients recovery (biofertilizer production). Additionally, both alternatives were compared to a typical small-sized activated sludge system. An economic assessment was also performed. The results showed that HRAP system coupled with biogas production appeared to be more environmentally friendly than HRAP system coupled with biofertilizer production in the climate change, ozone layer depletion, photochemical oxidant formation, and fossil depletion impact categories. Different climatic conditions have strongly influenced the results obtained in the eutrophication and metal depletion impact categories. In fact, the HRAP system located where warm temperatures and high solar radiation are predominant (HRAP system coupled with biofertilizer production) showed lower impact in those categories. Additionally, the characteristics (e.g. nutrients and heavy metals concentration) of microalgal biomass recovered from wastewater appeared to be crucial when assessing the potential environmental impacts in the terrestrial acidification, particulate matter formation and toxicity impact categories. In terms of costs, HRAP systems seemed to be more economically feasible when combined with biofertilizer production instead of biogas. On the whole, implementing HRAPs instead of activated sludge systems might increase sustainability and cost-effectiveness of wastewater treatment in small communities, especially if implemented in warm climate regions and coupled with biofertilizer production.

Valorization of a pharmaceutical organic sludge through different composting treatments

Nowadays, the agricultural reuse of pharmaceutical sludge is still limited due to environmental and agronomic issues (e.g. low stabilization of the organic matter, phytotoxicity). The aim of the present study was to evaluate the characteristics of a pharmaceutical sludge derived from the daptomycin production and to study the possibility of improving its quality through composting. The pharmaceutical sludge showed high content of macronutrients (e.g. total Kjeldahl N content was 38 g kg^-1), but it was also characterized by high salinity (7.9 dS m^-1), phytotoxicity (germination index was 36.7%) and a low organic matter stabilization. Two different mixtures were prepared (mixture A: 70% sludge + 30% wood chips w/w, mixture B: 45% sludge + 45% wood chips + 10% cereal straw w/w) and treated through static composting using two different aeration systems: active and passive aeration. The mixtures resulted in the production of two different compost, and the evolution of process management parameters was different. The low total solids and organic matter content of mixture A led to the failure of the process. The addition of cereal straw in mixture B resulted in increased porosity and C/N ratio and, consequently, in an optimal development of the composting process (e.g. the final organic matter loss was 54.1% and 63.1% for the passively and actively aerated treatment, respectively). Both passively and actively aerated composting of mixture B improved the quality of the pharmaceutical sludge, by increasing its organic matter stabilization and removing phytotoxicity.

Evaluation of benefits and risks associated with the agricultural use of organic wastes of pharmaceutical origin

Industrial fermentations for the production of pharmaceuticals generate large volumes of wastewater that can be biologically treated to recover plant nutrients through the application of pharmaceutical-derived wastes to the soil. Nevertheless, benefits and risks associated with their recovery are still unexplored. Thus, the aim of the present work was to characterize three potential organic residues (sludge, anaerobic digestate and compost) derived from the wastewater generated by the daptomycin production process. The main parameters evaluated were the physico-chemical properties, potential contaminants (heavy metals, pathogens and daptomycin residues), organic matter stabilization and the potential toxicity towards soil microorganisms and plants. The results showed that all the studied materials were characterized by high concentrations of plant macronutrients (N, P and K), making them suitable for agricultural reuse. Heavy metal contents and pathogens were under the limits established by European and Italian legislations, avoiding the risk of soil contamination. The compost showed the highest organic matter stabilization within the studied materials, whereas the sludge and the anaerobic digestate were characterized by large amounts of labile organic compounds. Although the pharmaceutical-derived fertilizers did not negatively affect the soil microorganisms, as demonstrated by the enzymatic activities, the sludge and the anaerobic digestate caused a moderate and strong phytotoxicity, respectively. The compost showed no toxic effect towards plant development and, moreover, it positively affected the germination and growth in lettuce and barley. The results obtained in the present study demonstrate that the valorization of pharmaceutical-derived materials through composting permits their agricultural reuse and also represents a suitable strategy to move towards a zero-waste production process for daptomycin.

Integrating microalgae tertiary treatment into activated sludge systems for energy and nutrients recovery from wastewater

In this study, microalgae digestate and secondary effluent were used to grow microalgae in a tertiary wastewater treatment, and then, the biomass was co-digested for biogas generation. A 30L closed-photobioreactor was used for microalgae cultivation. The biomass, mainly composed by Scenedesmus sp., reached and maintained a concentration of 1.1gTSS/L during 30days. A complete removal of N-NH₄⁺ and P-PO₄^3- and high nitrates and organic matter removals were achieved (58% N-NO₃^- and 70% COD) with 8d of HRT. The potential biogas production of the cultivated microalgae was determined in batch tests. To improve their biodegradability, a novel method combining their co-digestion with activated sludge after a simultaneous autohydrolysis co-pretreatment was evaluated. After the co-pretreatment, the methane yield increased by 130%. Thus, integrating microalgae tertiary treatment into activated sludge systems is a promising and feasible solution to recover energy and nutrients from waste, improving wastewater treatment plants sustainability.

Co-digestion of chicken manure and microalgae Chlorella 1067 grown in the recycled digestate: Nutrients reuse and biogas enhancement

The present investigation targeted on a sustainable co-digestion system: microalgae Chlorella 1067 (Ch. 1067) was cultivated in chicken manure (CM) based digestate and then algae biomass was used as co-substrate for anaerobic digestion with CM. About 91% of the total nitrogen and 86% of the soluble organics in the digestate were recycled after the microalgae cultivation. The methane potential of co-digestion was evaluated by varying CM to Ch. 1067 ratios (0:10, 2:8, 4:6, 6:4, 8:2, 10:0 based on the volatile solids (VS)). All the co-digestion trials showed higher methane production than the calculated values, indicating synergy between the two substrates. Modified Gompertz model showed that co-digestion had more effective methane production rate and shorter lag phase. Co-digestion (8:2) achieved the highest methane production of 238.71mL⋅(g VS)^-1 and the most significant synergistic effect. The co-digestion (e.g. 8:2) presented higher and balanced content of dominant acidogenic bacteria (Firmicutes, Bacteroidetes, Proteobacterias and Spirochaetae). In addition, the archaea community Methanosaeta presented higher content than Methanosarcina, which accounted for the higher methane production. These findings indicated that the system could provide a practicable strategy for effectively recycling digestate and enhancing biogas production simultaneously.