Municipal Biowaste Research Articles

Microplastic contamination of soil: Are input pathways by compost overridden by littering?

Compost application is a widely recommended agricultural practice to improve soil fertility. As almost all compost is likely polluted with plastic we hypothesize that compost application is a major input pathway for microplastics (MPs) into agricultural soil. To attribute the plastic load of soil to compost application, we investigated MPs in topsoil (0–30 cm) of a controlled, long-term fertilizer trial with application of compost made of municipal biowaste (0, 5, 10, and 20 t ha−1a−1), which ended 11 years ago. Microplastics were analyzed via density separation (ZnCl2) and light microscopy; testing this method recovered 92 ± 10 % of spiked plastic items. The fields of the long-term compost trial showed a MP load of 0–64 items kg−1, corresponding to MP stocks in the plough layer (0–30 cm) that ranged from 38.2 ± 55.5 million to 171.4 ± 57.5 million items ha−1. Microplastic stocks and contents increased with increasing amount of compost application. Thus, we confirm compost as a major input pathway for MPs into agricultural soil, with the effect still visible after 11 years. Comparison of calculated plastic input based on MP contents of recent German compost with MP loads found in soil revealed that overall compost application explained <6 % of total MP stocks. We assume that compost applied in earlier days contained higher plastic loads than recent ones, reflecting current awareness and successful efforts in reducing plastic loads during compost production. However, as the plots at the border of the field had up to 18 times higher MP loads than the inner plots of the trial, we suggest that littering also contributed significantly to MP pollution. Thus, even if given compost applications still add plastics to environment, other sources such as littering can already have become the dominating input pathway.

Microplastic Contamination of Composts and Liquid Fertilizers from Municipal Biowaste Treatment Plants: Effects of the Operating Conditions

High-caloric-value household biowaste is an attractive substrate for the production of biogas and fertilizer. Most household biowaste is contaminated by plastics, typically in the form of bags and foils from packaging. Operators of municipal biowaste treatment plans take great care to remove these contaminants, often at the cost of reducing the organic material entering the process. This study compares the residual plastic contamination of fertilizer (composts, digestates) from biowaste treatment plants with compost produced from greenery and digestates produced by agricultural biogas plants processing manure and energy crops. While the fertilizers from the agricultural biogas plants and greenery composts were minimally contaminated by plastic, we found considerable numbers of plastic fragments in the composts/fertilizers from the biowaste treatment plants. Moreover, while certainly being influenced by the quality of the incoming biowaste, this residual contamination appeared to depend largely on the operating conditions. In particular, shredding of the incoming material increased the degree of contamination. Sieving was an efficient method for the removal of fragments > 5 mm but was less efficient for the removal of smaller fragments. In view of the number of the recovered fragments in that size range, it is likely that still none of the finished composts surpassed the current dry weight limits imposed for the plastic contamination of high-quality composts with fragments > 1 mm in Europe (0.3% of dry weight) nor even in Germany (0.1% of dry weight). The contamination of the liquid fertilizer produced via anaerobic digestion by three of the investigated biowaste treatment plants (up to 10,000 particles with a size between 10 and 1000 μm−1) may pose a more serious concern.Graphical

Evaluation of Agricultural Value of Composts Prepared from Municipal Biowastes in Different Conditions of Composting Process

The increasing mass of organic waste as well as the assumptions of a circular economy enforce the rational management of this type of waste. One method of recycling is composting, which makes it possible to use waste efficiently as an organic fertilizer. This paper presents the results of a comparative study of six different composts in terms of their agricultural quality. The aim of this study was to evaluate the bioavailable amounts of metals using single extractions with DTPA solution and to characterize various humic compounds. Particular attention was paid to the amounts of labile carbon (LC), hot water-extractable carbon (HWC), and the quantity and quality of humus substances (HS). Regardless of compost types, they were characterized by a small share of easily decomposable compounds such as fulvic acids (FAs), LC, and HWC, which may indicate the low susceptibility of compost humic substances to microbiological degradation in soil. In general, the bioavailable metal amounts found in the analyzed composts were low; therefore, the tested composts applied to the soil can be considered safe for the environment.

Embedding circularity into the transition towards sustainable agroforestry systems in Peru

Peru is promoting the adoption of agroforestry systems with the aim to halt the deforestation of tropical forests caused by smallholder farmers. However, deficient soil conservation practices and nutrient management are common among the targeted smallholders, hampering the success of this strategy. In this study, we explore the potential of valorizing municipal biowaste as compost to be used as soil amendment in coffee agroforestry systems and in silvopastoral systems. The analysis was concentrated in four Peruvian regions and the most populous city in each of them. For lands with coffee production, it was assumed that 90 kg N ha−1 (i.e., 50% of the N requirements) should come from compost, while for pastures, the requirement was 40 kg P ha−1. We found that composting could lead to large greenhouse gas (GHG) reductions compared with the current waste disposal methods (i.e., deep dumping and landfilling), as it only emits 5–10% of the GHG emissions produced with the other methods. Nonetheless, the area of agroforestry and silvopastoral systems that could be fertilized with compost obtained from the main city of each region is limited and insufficient. If all compost were to be used for the coffee agroforestry system, less than 3% of the coffee agroforestry area could be fertilized, while in the case of pastures, only 4% would be attained. Large amounts of compost could be obtained from Lima, the most populated city; however, its transportation to the agroforestry areas would increase compost GHG emissions by 15–60%. Although composting municipal food waste and loss may bring GHG benefits and should be promoted, its use as a fertilizer requires mixing with N-rich sources to improve its nutrient quality.

Municipal biowaste treatment plants contribute to the contamination of the environment with residues of biodegradable plastics with putative higher persistence potential

Biodegradable plastics (BDP) are expected to mineralize easily, in particular under conditions of technical composting. However, the complexity of the sample matrix has largely prevented degradation studies under realistic conditions. Here composts and fertilizers from state-of-the-art municipal combined anaerobic/aerobic biowaste treatment plants were investigated for residues of BDP. We found BDP fragments > 1 mm in significant numbers in the final composts intended as fertilizer for agriculture and gardening. Compared to pristine compostable bags, the recovered BDP fragments showed differences in their material properties, which potentially renders them less prone to further biodegradation. BDP fragments < 1 mm were extracted in bulk and came up to 0.43 wt% of compost dry weight. Finally, the liquid fertilizer produced during the anaerobic treatment contained several thousand BDP fragments < 500 µm per liter. Hence, our study questions, if currently available BDP are compatible with applications in areas of environmental relevance, such as fertilizer production.

An economical source for peroxidase: maize cobs

According to the current situation of peroxidase (POD), the relevant studies on this enzyme indicated its importance as a tool in clinical biochemistry and different industrial fields. Most of these studies used the fruits and vegetables as source of this enzyme. So that in order to couple the growing requirements for POD with the recent demands for reduc-ing disposal volume by recycling the plant waste, the aim of the present study was to extract POD through management of municipal bio-waste of Iraqi maize species. A simple, green and economical method was used to extract this enzyme. Our results revealed that maize cobs are rich sources of POD, where the activity of this enzyme was found to be 7035.54 U/g of cobs. In pilot experiments this enzyme was extracted from the cobs using an efficient extraction buffer with either Cetyl Trimethyl Ammonium Bromide (CTAB), or sonication. To purify the extracted enzyme the previous step was followed by aqueous two phase extraction (ATPE) using 20% (w/v) polyethylene glycol (PEG) and 9% (w/v) ammonium sulfate. The obtained results indicated that POD was partially purified with 2.36 fold of purification and 81.78% recovery. The optimum temperature and pH of the extracted POD activity as well as the enzyme thermal stabil-ity were determined and found to be 20°C, pH 6, and stable at 60°C for 10 minutes respectively. Out of the present study findings, it can be concluded that maize cobs are rich source for POD and the applied protocol could be poten-tially used for POD extraction with high level. Meantime, this study suggested a new strategy by which the environ-mental pollution results from accumulation of plant waste can be reduced.

An 18-year field experiment to assess how various types of organic waste used at European regulatory rates sustain crop yields and C, N, P, and K dynamics in a French calcareous soil

Recycling organic waste (OW) in agriculture can improve soil fertility and substitute chemical fertilizers depending on the OW and their treatment. The effects of OW have often been studied in simplified cropping systems to strengthen the observed effects. The objective of this study was thus to evaluate the long-term effects of different types of OW used at European regulatory rates on C storage, crop yields and N, P, and K dynamics. OW has been applied every 2 years at 170 kg N ha-1 since 2001 in the long-term field experiment PROspective in northeastern France on a silty loam calcosol. The 5 types of OW included urban sewage sludge (SLU), green waste and SLU compost (GWS), municipal biowaste compost (BIO), farmyard manure (FYM), and composted FYM (FYMC). The control treatment (CON) did not receive any OW. All treatments were studied after applying (N + ) or not applying (N-) mineral N fertilization at an annual optimal rate. Biowaste digestate was also applied after 2014 in N- treatments. OW application increased crop yield compared with the unfertilized control. Mineral N fertilizer partially substituted by OW allowed crop yield to be sustained compared with mineral fertilizer only, saving 18–54% mineral N fertilizer, 56–80% mineral P fertilizer and 14–76% mineral K fertilizer. No effects on crop grain N, P and K concentrations were found. The efficiency of OW to maintain SOC, total N, Olsen-P and exchangeable K contents in soils greatly varied with the type of OW. Except for SLU, the SOC stocks significantly increased from + 2.9 to + 7.0 t SOC ha-1 for FYMC_N- and BIO_N-, respectively. SLU and digestate had the greatest N fertilizer replacement value (58% and 69%, respectively). N-leaching risk did not increase with OW application in the long term. For a positive ∆P of 100 kg ha-1, Olsen-P increased by 2 mg P kg-1 in the GWS_N- and SLU_N- treatments, whereas Olsen-P decreased in other treatments. A surplus of + 100 kg ha-1∆K raised the exchangeable K stock by 20 and 21 kg K ha-1 in the FYM_N- and FYMC_N- treatments, respectively, whereas exchangeable K decreased in the BIO and GWS treatments. Our results highlight the ability of all tested types of OW to sustain crop yields in the long term when used at EU regulatory rates, while their effects on mineral fertilizer savings, SOC, soil mineral N, Olsen-P, and exchangeable K contents greatly varied according to the considered OW.

Neglected effect of transportation on the property of municipal biowaste and the subsequent biomethane potential

Long-distance transportation of municipal biowaste can influence its physio-chemical characteristics and the subsequent anaerobic digestion (AD) performance. However, the effect of whole transportation processes on the characteristics of municipal biowaste from upstream source separation/collection to downstream storage remains poorly documented. To this end, this study presented the relevant work by sampling in practical conditions. Results showed that transportation led to a high hydrolysis rate of 33.4%–35.5%, and an acidification rate of 15.8%–17.3%. Simultaneously, lactic acid was produced to a concentration of 18.1 g/L, occupying approximately 20% of dissolved organic carbon. Furthermore, the highest cumulative CH4 production was observed at the samples of source separation/collection (398 ± 52–519 ± 117 mL/gVS for FW, 276 ± 51–332 ± 41 mL/gVS for KW), and then accompanied by a decrease (299 ± 31 mL/gVS for FW and 285 ± 39 mL/gVS for KW) after downstream storage. The results indicated that the subsequent anaerobic digestion would be inclined to appear perturbation caused by the lactic acidification of the initial feed and it is imperative to avoid further conversion of lactic acid to propionic acid, which could provide vital guideline reference for the optimization of biogas production process. Moreover, the lactic acid-rich property also highlights other value-added pathways for the resource recovery of municipal biowaste.

Application of organic wastes to soils and legislative intricacies in a circular economy context

Currently, the absence of specific regulations on soil fertilization gives rise to sectorial normative with different regional approaches regarding application conditions, quality and other conditions that reused materials must meet. The purpose of this case study in Galicia (NW Spain) is to analyse the coherence of legal texts in the application of organic waste in soils regarding a more circular economy. The context of the case study is characterized by several Directives such as the Nitrates Directive or the "out of date" Directive on sewage sludge, among others, the lack of soil quality protection regulations and the existence of different administrative levels (European Union, Member State and Region). Manures and other agriculture wastes represent the main source of wastes being vastly applied to soils without previous treatment. Other waste streams (i.e. industrial biowaste, municipal biowaste and sewage sludge) undergo treatment generating commercial fertilizers, biostabilized wastes, technosols and waste-treated products that are subject to different standards. The screening of regulations and scientific literature detected limiting situations in the recycling of organic wastes due to natural or legal issues. On the other hand, risky applications are identified due to the lack of quality requirements for waste-treated products under regional legislation, or no mandatory compliance with codes of good agricultural practices for manures and waste-treated products. Contradictory situations of legal regulations and other issues were outlined and discussed. Final considerations were outlined to promote a more effective recycling of organic wastes and the design of a suitable legislation adapted to the natural conditions of the region.Graphical abstract

Waste Biopolymers for Eco-Friendly Agriculture and Safe Food Production

This work addresses environmental problems connected with biowaste management, the chemical industry, and agriculture. These sectors of human activity cause greenhouse gas (GHG) emissions in the air, climate change, leaching of excess mineral fertilizers applied to soil into ground water, and eutrophication. To mitigate this problem in agriculture, controlled release fertilizers (CRFs) are made by coating mineral fertilizers granules with synthetic polymers produced from the fossil-based chemical industry. This strategy aggravates GHG emission. In the present work, six formulations containing sunflower protein concentrate (SPC) and a new biopolymer (BP) obtained from sunflower oil cake and by hydrolysis of municipal biowaste, respectively, and commercial urea were tested as CRFs for spinach cultivation against the control growing substrate Evergreen TS and commercial Osmocote®. The results show large differences in plants’ nitrate concentration due to the different treatments, although the same nitrogen amount is added to the substrate in all trials. BP is the key component mitigating nitrate accumulation in plants. The plants grown in the substrates containing BP together with SPC and/or urea, although exhibiting relatively high total N uptake (47–52 g kg−1), have significantly lower nitric to total N ratio (9.6–12.0) than that (15.3–16.5) shown by the plants grown in the substrates containing SPC and/or urea, but no BP. The data confirm that all composites containing BP yield the safest crop coupled with high biomass production. Replication of BP effects for the cultivation of different plants will contribute to the development of a biobased chemical industry exploiting biowastes as feedstock.

Integrated chemical and biochemical technology to produce biogas with a reduced ammonia content from municipal biowaste. Validating lab-scale research in a real operational environment

A virtuous biowaste cycle replicated in three industrial sites (Italy, Greece and Cyprus) yielding value added products (SBO) for agriculture and chemicals' bioeconomy. A cofunded LIFE project.

Mechanical pre-treatment of source-collected municipal biowaste prior to energy recovery by anaerobic digestion

Pre-treatments are usually necessary to prepare biowaste to anaerobic digestion. The major objectives are (i) to remove undesirable materials such as plastics and metals, which may contaminate the biowaste even if separated source-collection systems are implemented, and (ii) to extract the most readily biodegradable organic fractions from the waste stream. In this study, two wet mechanical pre-treatments, namely air-compressed press and worm screw press, were investigated on urban household biowaste. Two liquid to solid ratios were tested in each pre-treatment. Anaerobic digestion of pre-treated biowaste was studied by measuring their biomethane potentials and by controlled experiments in a continuously stirred-tank reactor with a feed load of 3.5 gVS.L−1.d−1. It was observed that increasing liquid to solid ratio in the pre-treatments allowed to increase the proportion of biodegradable organic matter extracted from the biowaste, up to 949 gCOD.kgTS−1 from household biowaste. The biomethane potentials of pre-treated waste were very high (up 525 LCH4.kgVS−1) and COD (949 gCOD.kg−1TS) from household biowaste. Anaerobic digestion in continuously stirred-tank reactor showed a very strong conversion of COD load (81%) and a high methane production up to 345 LCH4.kgVS−1.

Extraction and Identification of a Wide Range of Microplastic Polymers in Soil and Compost.

Microplastic pollution is globally widespread; however, the presence of microplastics in soil systems is poorly understood, due to the complexity of soils and a lack of standardised extraction methods. Two commonly used extraction methods were optimised and compared for the extraction of low-density (polyethylene (PE)) and high-density microplastics (polyethylene (PET)), olive-oil-based extraction, and density separation with zinc chloride (ZnCl2). Comparable recoveries in a low-organic-matter matrix (soil; most >98%) were observed, but in a high-organic-matter matrix (compost), density separation yielded higher recoveries (98 ± 4% vs. 80 ± 11%). Density separation was further tested for the extraction of five microplastic polymers spiked at different concentrations. Recoveries were >93% for both soil and compost, with no differences between matrices and individual polymers. Reduction in levels of organic matter in compost was tested before and after extraction, as well as combined. Double oxidation (Fenton’s reagent and 1 M NaOH) exhibited the highest reduction in organic matter. Extracted microplastic polymers were further identified via headspace solid-phase microextraction–gas chromatography–mass spectrometry (HS-SPME–GC–MS). This method has shown the potential for descriptive quantification of microplastic polymers. A linear relationship between the number of particles and the signal response was demonstrated for PET, polystyrene (PS), polyvinyl chloride (PVC), and PE (R2 > 0.98 in alluvial soil, and R2 > 0.80 in compost). The extraction and identification methods were demonstrated on an environmental sample of municipal biowaste compost, with the recovery of 36 ± 9 microplastic particles per 10 g of compost, and the detection of PS and PP.

Evaluation and Acceleration of Municipal Biowaste Compost Production and its Effect on Growth and Yield of Amaranthus

To limit the accumulation of municipal solid waste, quick solid waste management techniques are more vital to reuse, reduce, and recycle the Municipal Solid Wastes MSW). A study was conducted to shorten the composting time and assess the degradation efficiency of different micro consumers in Municipal Solid Waste Compost (MSWC) production and followed by a field experiment with Amaranthus as a test crop to evaluate the influence of MSWC on crop yield. Various sources viz., Saw dust balls impregnated with Panchakavya solution, TNAU Biomineralizer, PUSA decomposer, Effective Microorganisms (EM) solution, RCOF Waste decomposer and Novel microbial consortia were used for rapid production of biowaste compost. The results showed that the PUSA decomposer and EM Solution significantly reduced the period of composting to 35 and 37 days respectively. The nutrient parameters of compost viz., C:N ratio (13:1), total N (3.37%), total P (0.14%) and total K (0.65%) were better in the compost prepared with PUSA decomposer followed by those with EM solution and novel microbial consortia. The bio compost obtained from this study was utilized in the field experiment to assess the biomass production of Amaranthus. Enriched MSWC @ 5t ha-1 + 75% NPK produced greater amount of biomass (27.84 t ha-1), in comparison with control which produced 59.7% higher biomass yield. The overall results indicated that proper microbial inoculation of solid biowastes shortened the duration of composting and combined application of municipal biowaste compost with inorganic fertilizers saved 25 percent of fertilizer dosage, improved the soil quality and crop yield thus ensuring ecofriendly disposal of wastes.

Biowaste-Derived Humic-like Substances Improve Growth and Quality of Orange Jasmine (Murraya paniculata L. Jacq.) Plants in Soilless Potted Culture

Humic-like substances (HLS) are among the most used biostimulants in agriculture as a means for improving plant growth, nutrient uptake, crop yield, and stress tolerance. HLS derived from municipal biowastes were applied as a substrate drench in order to evaluate their biostimulatory effect on the growth and ornamental quality of Orange Jasmine (Murraya paniculata L. Jacq.) potted plants. Two HLS, derived from the digestion of the organic humic fraction and from composting of a mix of sewage sludge digestate and gardening residues, were compared with a commercial leonardite-based product in the framework of a greenhouse experiment in soilless culture. The application of the two biowaste-derived HLS resulted in plants showing a 39.9%, 87.0%, 111.6%, 35.4%, 37.9%, 35.3%, and 81.3% increase in plant height, number of flowers and fruits, leaf production, total dry biomass, root length, and water use efficiency, respectively, compared to those treated with the commercial product and the untreated (control) plants. The enhanced growth performance of HLS-treated plants was due to the higher chlorophyll relative content (+24.2% on average) and net photosynthesis (+114.7% on average) of their leaves. The positive results obtained from the application of non-commercial HLS suggest that biowaste recycling is a sustainable and environment-friendly source of biostimulants, as an alternative to agrochemicals and existing leonardite-based plant biostimulants.

Integrated Chemical Biochemical Technology to Reduce Ammonia Emission from Fermented Municipal Biowaste

A new eco-friendly process is reported, the implementation of which at the EU level could reduce ammonia and greenhouse gas emissions from fermented biowaste by over 1 Gt yr–1. The present work reports the case study of municipal biowaste (MBW). The process is based on the use of soluble bio-organic substances (SBOs) as auxiliaries in the anaerobic fermentation of MBW to produce biogas and digestate with reduced ammonia content. The SBO-assisted process enables a virtuous biowaste cycle, where MBW is sequentially fermented under anoxic conditions, the digestate is composted, and the compost generated is hydrolyzed, yielding SBO, which is recycled to the anaerobic fermentation reactor at 0.2% concentration. The results show that depending on the MBW source, fermentation inoculum, and SBO concentration in the fermentation slurry, about 40% reduction of ammonium in the digestate is achieved, whereas the control fermentation without SBO exhibits up to 11% ammonia increase. The microbial community and biogas production are not significantly affected by SBO addition. The data are consistent with biological and chemical processes occurring in SBO-assisted fermentation. These comprise ammonia production by protein hydrolysis catalyzed by proteolytic bacteria and ammonia oxidation to N2 catalyzed by SBOs. The results confirm the benefit provided by the use of SBOs to reduce the environmental impact of biowaste. These encourage the implementation of SBO-assisted fermentation in the real operational environment.

Anaerobic digestion of biowaste in Indian municipalities: Effects on energy, fertilizers, water and the local environment

Anaerobic digestion (AD) of biowaste seems promising to provide renewable energy (biogas) and organic fertilizers (digestate) and mitigate environmental pollution in India. Intersectoral analyses of biowaste management in municipalities are needed to reveal benefits and trade-offs of AD at the implementation-level. Therefore, we applied material flow analyses (MFAs) to quantify effects of potential AD treatment of biowaste on energy and fertilizer supply, water consumption and environmental pollution in two villages, two towns and two cities in Maharashtra. Results show that in villages AD of available manure and crop residues can cover over half of the energy consumption for cooking (EC) and reduce firewood dependency. In towns and cities, AD of municipal biowaste is more relevant for organic fertilizer supply and pollution control because digestate can provide up to several times the nutrient requirements for crop production, but can harm ecosystems when discharged to the environment. Hence, in addition to energy from municipal biowaste - which can supply 4-6% of EC - digestate valorisation seems vital but requires appropriate post-treatment, quality control and trust building with farmers. To minimize trade-offs, water-saving options should be considered because 2-20% of current groundwater abstraction in municipalities is required to treat all available biowaste with 'wet' AD systems compared to <3% with 'dry' AD systems. We conclude that biowaste management with AD requires contextualized solutions in the setting of energy, fertilizers and water at the implementation-level to conceive valorization strategies for all AD products, reduce environmental pollution and minimize trade-offs with water resources.

Mechanical pretreatment of municipal biowaste to produce an aqueous slurry dedicated to anaerobic digestion.

The present study investigated a wet mechanical pretreatment to improve methane production by anaerobic digestion from biowaste material by separating a biodegradable aqueous slurry fraction (ASF) from a more recalcitrant particulate fraction (PF). Four source-sorted municipal biowastes were studied, namely household (HBW), supermarket (SBW), restaurant (RBW), and green biowaste (GBW). The treatment consisted in soaking the waste in water and then pressing the slurry through a grid with 3-mm openings to separate the two fractions. Methane production of ASF and PF obtained from the four biowastes were measured using the BMP protocol and compared to the potential of the respective untreated biowaste. Results were very different for GBW as compared to the other three BWs. With GBW, which was the most lignocellulosic of the BW studied, only 17% of the initial methane potential was recovered in the ASF. The extraction was much better on the other biowastes and increased in the following order: HBW (58%)≃RBW (57%) < SBW (67%). The ASF from these biowastes exhibited low total solid contents and high BMPs (416, 408, and 423 NLCH4.g-1vs for HBW, RBW, and SBW respectively). The experimental results obtained in this study therefore showed that wet pressing separation was an efficient pretreatment to improve and facilitate methane production by anaerobic digestion of biowaste such as HBW, RBW, and SBW.

A New Composite Biomaterial Made from Sunflower Proteins, Urea, and Soluble Polymers Obtained from Industrial and Municipal Biowastes to Perform as Slow Release Fertiliser

Controlled-release fertilizers (CRF) are needed under current agriculture practice to decrease the environmental impact caused by fertilizer doses applied in excess of plants’ uptake rate. Commercial CRF are available. They are manufactured from mineral fertilizers encapsulated into a synthetic polymer matrix or coated by a polymer layer. However, substitution of fossil sourced organic polymers with biopolymers is a major environmental concern. In the present paper, we describe the manufacture by a continuous twin-screw extrusion process, and the mechanical and chemical properties of injection-molded composite pellets containing 90% sunflower protein concentrate (SPC) matrix, and 5–10% of a biopolymer (BP) obtained from municipal biowastes (MBW), and/or urea (U). The reported results show that SPC-BP-U behaves as an efficient eco-friendly CRF. BP contributes to several benefits to the performance of the composite pellets, upon increasing surface hardness, and controlling the formation of ammonia from urea hydrolysis and the release of organic nitrogen. The SPC-BP-U appears a powerful eco-friendly CRF to supply organic C and the three major N, P, and K nutrients to soil and plants. It offers worthwhile scope for being tested in the cultivation of specific plants under the real operational conditions of agriculture practices.

Long-term operation of the pilot scale two-stage anaerobic digestion of municipal biowaste in Ho Chi Minh City

A pilot-scale two-stage anaerobic digestion system, which includes a feed tank (0.4 m3), a hydrolysis reactor (1.2 m3) followed by a methane fermenter (4.0 m3) was set up and run at the municipal solid waste landfill located in Ho Chi Minh City (HCMC), Vietnam. The feed that was separated from urban organic solid waste was collected at households and restaurants in District 1, HCMC. This study aimed to investigate the resource recovery performance of the pilot two-stage anaerobic digestion system, in terms of carbon recovery via biogas production and nutrient recovery from digestate. The average organic loading rate (OLR) of the system was step increased from 1.6 kg volatile solids (VS)·m−3·d−1, 2.5 kg VS·m−3·d−1 and 3.8 kg VS·m−3·d−1 during 400 days of operation. During the long-term operation at three OLRs, pH values and alkalinity were stable at both hydrolysis and methanogenesis stages without any addition of alkalinity for the methanogenesis phase. High buildup of propanoic acid and total volatile fatty acid concentrations in the fermenter did not drop pH values and inhibit the methanogenic process at high OLRs (2.5–3.8 kg VS m−3·d−1). The obtained total chemical oxygen demand (tCOD) removal performance was 83–87% at the OLRs ranging from 2.5 kg VS·m−3·d−1 and 3.8 kg VS·m−3·d−1, respectively. The highest biogas yield of 263 ± 64 L·kg−1 tCOD removed obtained at OLR of 2.5 kg VS·m−3·d−1. It is expected that a full scale 2S-AD plant with capacity of 5200 tons day−1 of biowaste collected currently from municipal solid waste in HCMC may create daily electricity of 552 MWh, thermal energy of 630 MWh, and recovery of 16.1 tons of NH4+-N, 11.4 tons of organic-N, and 2.1 tons of TP as both organic liquid and solid fertilizers.