Biowaste Compost Research Articles

Suitability of Biowaste and Green Waste Composts for Organic Farming in Germany and the Resulting Utilization Potentials

In this study, the suitability of biowaste and green waste composts in organic farming is presented based on quality assurance data of approximately 21,000 compost analyses from 2015 to 2020. The evaluation of compost suitability was based on both the legal regulations of the EU 2021/1165 and the requirements of the two largest German organic farming associations Bioland and Naturland. In 2020, 70.1% of the composts agreed with the above-mentioned regulations, 21.6% exceeded the limits for heavy metals and 7.3% exceeded the limits for foreign matter. The negative influence of the single elements regarding the suitability of composts for organic agriculture declined in the order Zn > Pb > Cd > Ni > Cu. In the bio-waste composts, the impurity content subsequently decreased by more than 50% from 2015 to 2020. In 2019 and 2020, approximately 2.5 million Mg fresh mass (FM) of the analyzed composts were suitable for organic farming. With an average compost application of 5 Mg FM per hectare (ha) and year, about 500,000 ha of arable land could have been supplied in 2020.

Specific and Intraspecific P Efficiency of Small-Grain Legumes as Affected by Long-Term P Management

Legumes have a high demand for phosphorus (P) but also have effective physiological and morphological strategies of P mobilisation. In order to evaluate the inter- and intraspecific P efficiency of small-grain legumes under contrasting long-term P management, eight accessions each of alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.) were cultivated in two consecutive growing periods from 2020 to 2021 in a field trial established in 1998. Six treatments (no P, triple-superphosphate (TSP), biomass ash, cattle manure, biowaste compost, and biowaste compost + TSP) were considered as P sources. While the yield clearly varied between both growing seasons, the differences between alfalfa and red clover were relatively small (4.7 vs. 4.9 Mg ha−1 in 2020 and 12.0 vs. 10.5 Mg ha−1 in 2021, p < 0.05). Even after more than 20 years of P management, crop yields were hardly affected by mineral P sources (TSP and biomass ash) while organic fertilisers increased the yields and nutrient uptake of plants and also raised soil P pools and the activities of soil enzymes in comparison to the control. A relevant crop effect was only found for the nitrogen (N) leaching with higher mineral N contents in 60 to 90 cm soil depth measured for red clover compared to alfalfa (11.8 vs. 4.8 kg ha−1, p < 0.05). Our results emphasise the high P efficiency of small-grain legumes without pronounced inter- or intraspecific differences. The yield-enhancing effect of organic amendments was related to higher soil fertility rather than to P supply.

Uncovering Bacterial Diversity during Mesophilic and Thermophilic Phases of Biowaste Composting through Next-Generation Sequencing

The accumulation of biowastes is one of the main concerns of modern society. One of the most environmentally friendly solutions to convert biowaste into a product is composting. Biowastes may contain unknown substances that are persistent in the final compost, thus contributing to soil contamination and salinization. The effectiveness of the composting process depends on the microbial communities involved, which is the number of investigations’ targets. The present work studied the bacterial diversity of mesophilic and thermophilic phases of composting developed in two different sites. The study was conducted through next-generation Illumina HiSeq sequencing and phylogenetic communities, revealing the dynamics and changes in specific mesophilic and thermophilic habitats of composting piles. The results showed a higher number of bacterial species in the mesophilic phase than in the thermophilic one, proved by the Shannon and Chao indices. In addition, the diversity of bacterial species expressed by the operational taxonomic units was much higher at the site of Harmanli than at the Yasno pole. Higher abundance was found of the genera Sphingobacterium, Sphingomonas, Paracoccus, Pseudomonas, and Halomonas in both studied sites. In the compost of Harmanli genera Streptomyces, Truepera, and Flavobacterium were found to be much more abundant compared to the compost of the Yasno pole. Finally, we conclude that the two plots show relatively significant differences in the diversity of bacteria during biowaste composting. Substantial differences were also observed between the mesophilic and thermophilic phases, with the first showing a significantly higher degree of species richness.

A REVIEW ON MICROPLASTIC IN THE SOILS AND THEIR IMPACT ON SOIL MICROBES, CROPS AND HUMANS

For modern human life, since the beginning of the 21st century, plastic become indispensable. The golden period for the plastic industry was the second half of the 20th century when plastic-based products bucket to the car were manufactured. Due to mismanagement, and indiscriminate use microplastics are emerging as persistent terrestrial pollutants. In the last decade, environmental scientists and other stakeholders have paid serious attention to soil pollution by microplastics. In soils, the microplastic particles act as a vector for the toxic persistent organic pollutants and potentially toxic metals which are easily sorbed by plants and enter the food chain.Microplastic pollutants not only influence the soil’s physicochemical properties but also impact the feeding habits of soil biota. Microplastic in soils is due to sewage sludge, bio waste compost amendments, plastic mulching, wastewater irrigation, leachate from landfills and atmospheric deposition. The quantity of microplastic particles in the soils varied from nil to13000 items per kg of soil. The quantity of microplastic in the soil is 5-23 times that in the ocean. The microplastic in soil retards seed germination and plant growth. Enzymatic activities of the soil are also influenced by microplastic. Plastic Pellets, Personal Care Products and Cosmetics, Synthetic Textiles, the Abrasion of Tyres, City Dust, and the Abrasion of Road Markings etc. are the environmental sources of microplastic. Intake by humans via food causes respiratory toxicity, cytotoxicity, immunotoxicity and reproductive toxicity among other effects. The present work reports the sources and distribution of microplastic in the soil environment and their impact on soil biota, plants, and human health.

Does the timing of short-term biowaste compost application affect crop growth and potential nitrate leaching? The case studies of processing tomato and cauliflower under field conditions

The feasibility of municipal solid waste compost (MSWC) as a substitute for mineral nitrogen (N) fertiliser was tested for a spring-summer (i.e., processing tomato) and an autumn-winter (i.e., cauliflower) vegetable crop grown in Mediterranean open field conditions. Two different doses (10 and 20 t dm C ha–1) and two distribution timings for each dose (i.e., early application at about nine months before processing tomato transplanting and five months before cauliflower transplanting: C10_early and C20_early; late application at about one month before processing tomato and cauliflower transplanting: C10_late and C20_late) were compared in a two-year field experiment. An unfertilised control and a 100% mineral N fertilisation (MIN, 200 kg N ha–1 for processing tomato and 150 kg N ha–1 for cauliflower) were added to the experiment. The application of MSWC significantly reduced the aboveground DM accumulation compared to the MIN in both crops, and it was inadequate to ensure a high yield for spring-summer and autumn-winter vegetables. However, the timing of compost application seems to play an essential role in reducing the reduction of crop growth due to compost application. In both tomato and cauliflower, when the MSWC was applied a few months earlier than the transplanting (i.e., in the previous summer in tomato and the previous spring in cauliflower), the DM and yield reduction was less apparent than in soil where compost was applied immediately before transplanting. Despite the lowest N-uptake associated with the MSWC application, the N-NO3 concentration in the soil solution was reduced by MSWC. In addition to the amendment effect, compost use may positively impact lowering N leaching risks in the groundwater. Combining the use of MSWC applied early before the crop season with mineral N fertiliser, it is possible to gain high yield, increase soil organic carbon and reduce groundwater contamination risk both in spring-summer and autumn-winter vegetable crops. Highlights- Biowaste compost decreased the aboveground biomass accumulation and yield in processing tomato and cauliflower. - Biowaste compost alone did not meet the N requirement in processing tomato and cauliflower. - Biowaste compost distribution in the summer before the processing tomato growing season alleviated its depressive effect in reducing DM and yield. - Biowaste compost distribution in the spring before the cauliflower growing season alleviated its depressive effect in reducing DM and yield. - Biowaste compost decreased the N-NO3 concentration in soil solution compared to mineral fertilisation with a positive effect in reducing N leaching risks in the groundwater.

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.

Electrocoagulation vs. Integrate Electrocoagulation-Natural Zeolite for Treatment of Biowaste Compost Leachate—Whether the Optimum Is Truly Optimal

Natural zeolites are well-known materials widely applied in the environmental remediation treatment process. However, the integration of various treatment methods is exceedingly investigated for achieving satisfactory effluent quality. In this paper, the integration of electrocoagulation and natural zeolite was evaluated in the treatment of biowaste compost leachate in a single step. The influence of different distances of electrodes (1.5, 3, and 4.5 cm), stirring speed (70, 200, and 400 rpm), the addition of natural zeolite and electrolyte NaCl on the efficiency of treatment of biowaste compost leachate has been carried out. Process efficiency was evaluated by measuring the change of pH value, electrical conductivity, temperature, turbidity, chemical oxygen demand (COD), total Kjeldahl nitrogen (TNK), total solids, and sludge settling test. The Taguchi method was applied to optimize biowaste compost leachate treatment. Experiments are planned according to Taguchi’s L8 (24 41) orthogonal array. The stirring speed, electrode distance, electrolyte and zeolite addition, solution initial pH adjustment were chosen as controllable factors, and their impact on COD, turbidity, TNK, settling rate, and electrode consumption were studied. Results show that optimal conditions depend on the parameter of interest and that optimal values for a particular parameter are not always the optimum if the desired goal is considered.

Biowaste composting process - comparison of a rotary drum composter and open container

Composting is recognized as a sustainable waste management approach in which microorganisms treat and stabilize biodegradable waste under aerobic conditions to obtain compost as a final product. In this paper, composting of biowaste in a rotary drum composter (closed system) and an open container (open system) was compared. Temperature, pH, electrical conductivity, a carbon-to-nitrogen mass ratio (C/N ratio) and contents of moisture, carbon and dry and volatile matter, were measured during composting. Results showed decreasing profiles for moisture, volatile matter, and carbon contents, as well as for the C/N ratio, while increasing profiles for the dry matter content and electrical conductivity during composting in both systems. Leachates were formed only during the first three days of composting and were characterized with high organic loads, high ammonia concentrations, low pH, and high conductivity and turbidity. The organic matter content data during the composting process were analysed according to the first order kinetic model. Results suggested that there was a difference in the rate of organic matter decomposition, which was higher when composting in the open vessel than in the rotary drum composter.

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.

Combination of Compost and Mineral Fertilizers as an Option for Enhancing Maize (Zea mays L.) Yields and Mitigating Greenhouse Gas Emissions from a Nitisol in Ethiopia

Combined application of organic and mineral fertilizers has been proposed as a measure for sustainable yield intensification and mitigation of greenhouse gas (GHG) emissions. However, fertilizer effects strongly depend on the soil type and still no precise information is available for Nitisols in Ethiopia. The study evaluated effects of different ratios of biowaste compost and mineral fertilizers (consisting of nitrogen (N), phosphorus (P), and sulphur (S)) on maize (Zea mays L. Bako-hybrid) yields in a two-year field trial. Soil samples from each treatment of the field trial were used to estimate emissions of nitrous oxide (N2O), carbon dioxide (CO2), methane (CH4), and microbial activity in a 28-day incubation experiment with two moisture levels (40% and 75% water-filled pore space, WFPS). The application of fertilizers corresponded to a N supply of about 100 kg ha−1, whereby the pure application of mineral fertilizers (100 min) was gradually replaced by compost. Maize yields were increased by 12 to 18% (p < 0.05) in the combined treatments of compost and mineral fertilizers compared to the 100 min treatment. The cumulative emissions of N2O and CO2 but not CH4 were affected by the fertilizer treatments and soil moisture levels (p < 0.05). At 75% WFPS, the N2O emissions in the 100 min treatment was with 16.3 g ha−1 more than twice as high as the treatment with 100% compost (6.4 g ha−1) and also considerably higher than in the 50% compost treatment (9.4 g ha−1). The results suggest that a compost application accounting for 40 to 70% of the N supply in the fertilizer combinations can be suitable to increase maize yields as well as to mitigate GHG emissions from Nitisols in Southwestern Ethiopia.

Influence of the Choice of Cultivar and Soil Fertilization on PTE Concentrations in Lactuca sativa L. in the Framework of the Regenerative Agriculture Revolution

Evaluating the relative weight of the choice of cultivar and soil fertilization on potentially toxic elements (PTEs) accumulation is crucial in promoting informed decisions in the framework of regenerative agriculture. To this end, 11 PTEs (Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Zn) were determined in both leaves and roots of six cultivars (Stylist, Xanadu, Aljeva, Bacio, Analena, Vincenzo) of lettuce (Lactuca sativa L.) grown side by side on mineral fertilized or biowaste compost amended soils, under greenhouse conditions. The use of multivariate and linear modelling approaches indicated that the organ and cultivar primarily account for the variability in PTE concentrations. In terms of PTE partitioning between organs, Cd and Mg were preferentially accumulated in leaves, whereas Cu, Pb, K and Zn in roots. As for the cultivar, Xanadu showed the highest concentrations of several PTEs, with Cd reaching concerning levels. Fertilization had a detectable contribution only on Cd accumulation, slightly increased in leaves by compost. Findings highlight the key role of cultivar choice in guaranteeing food safety and grant the possibility to adopt biowaste compost in regenerative agriculture without concerns about PTE accumulation enhancements in lettuce, but demand a cautionary approach in the case of Cd.

A seven-year experiment in a vegetable crops sequence: Effects of replacing mineral fertilizers with Biowaste compost on crop productivity, soil organic carbon and nitrates concentrations

The intensification of agriculture has been distorting the perception of fertility, with a great attention on its chemical component, reinforced by the use of chemical fertilizers as a major option to manage soil fertility. The consequent decline in soil organic matter content is a threat to the sustainability of intensive agricultural systems. Improving soil quality by increasing soil organic carbon (SOC) is seen as a potential way of improving crop yield and quality. In this paper, we studied the effects of two compost-based fertilization strategies on soil fertility and on yields of the following seven vegetable crops: eggplant (Solanum melongena L.), Endive (Cichorium endivia L.), Tomato (Lycopersicon lycopersicum (L.) Karsten Exfarw), Cauliflower (Brassica oleracea L), Onion (Allium cepa L. var. cepa), Muskmelon (Cucumis melo L), Fennel (Pheniculum vulgare L). The results of a seven-year experiment carried out under open field conditions in Southern Italy are presented. Four different fertilization treatments were applied: a) unfertilized control (CNT) b) supplying of mineral N, P2O5 and K2O by chemical fertilizers (CF); c) biowaste compost amendment at 30 Mg ha−1 year−1 as dry matter (d.m.) (≈ 8.4 Mg ha−1 organic C) in the first three years, and 15 Mg ha−1 year−1 as d.m. (≈ 4.2 Mg ha−1 organic C) from the fourth year onwards (Com); d) biowaste compost application of 15 Mg ha−1 year−1 as d.m. integrated with ½ of mineral N supplied in the mineral fertilization (ComN). We demonstrated that the loss of the productive ability in unfertilized control corresponded to SOC concentration ≤ 1%, the same occurred with CF fertilization where, however, the addition of chemical fertilizers concealed soil degradation. On the contrary, SOC concentration ranging between 1.2 and 1.4% in compost amended treatments granted vegetable crops yields always higher than or similar to mineral fertilization. Such SOC concentrations were far from the 2% threshold considered as the minimum SOC concentration of not degraded soil. SOC content increased 8.1 and 5.7 Mg ha−1 due to Com and ComN strategies. The supplying of 4-5 Mg C ha−1 year−1 as in ComN resulted in a positive efficiency (15%) in stabilizing C in soil compared to the supplying of higher doses as in Com. As concerns the risks of groundwater pollution due to N-NO3 releases in amended soils, we ascertained in three annual monitoring campaigns that releases measured in the 0-30 cm soil layer did not exceed values of 20-25 mg kg−1 considered as the treshold above which vegetable crop response to additional fertilization was unlikely .

Biowaste compost amendment modifies soil biogeochemical cycles and microbial community according to aggregate classes

The use of biowaste compost as soil organic amendment is of great interest for soil recovery. However, there is little knowledge of detailed effects on chemical, microbial, and biochemical properties in different soil compartments (aggregate classes) following long-term amendment with biowaste compost. We studied the distribution of soil organic carbon (SOC), total nitrogen (TN), soil microbial biomass (SMB), microbial community composition and activity in bulk soils and in three water stable aggregate classes (>250, 250–53, and <53 μm), after seven years of different fertilization treatments: biowaste compost (Com), mineral NPK fertilizers (Min), biowaste compost with half-dose N fertilizer (ComN), and no fertilizers as control (Cnt). Microbial biomass was assessed through a double-stranded DNA (dsDNA) based method and enzyme activities were determined using a microplate-based fluorometric assay. Denaturing gradient electrophoresis (DGGE) fingerprinting analysis was used to study the composition of both fungal and bacterial communities. Com and ComN treatments improved significantly SOC, TN and SMB in bulk soils and in all aggregate sizes. Composition of fungal and bacterial communities shifted with biowaste compost, more in soil aggregates than in bulk soils. To this change of microbial community composition in soil aggregates, corresponded a response of enzymes activities to fertilization treatments depending on aggregate size. Com treatment caused the highest enzyme activity in microaggregates (250–53 μm), whereas ComN and Min showed, in general, a higher activity in silt plus clay sized aggregates (<53 μm). The enzymes involved in biogeochemical cycle of P, with the exception of the phytase, displayed the lowest activity in macroaggregates (>250 μm), suggesting that the intensity of this cycle is lower in this soil niche; however, they increased with C accumulation due to both biowaste compost treatments. Furthermore, fungal diversity and richness decreased with fertilization treatments in all fraction except in macroaggregates. Thus, soil aggregates regulated the feedback of chemical, biochemical and microbial properties in response to soil fertilization strategies.

Water hyacinth (Eichhornia crassipes (Mart.) Solms.) as an alternative raw material for the production of bio-compost and handmade paper

Water hyacinth (WH) is considered as the worst aquatic weed in the world because of its rapid growth and fast spread into new areas of fresh water bodies. We investigated the potentiality of using WH as a raw material for production of handmade paper and compost in Bangladesh. Potash pulping was done using potassium hydroxide (KOH) at different alkali concentrations (8–12%) with a liquor to solid ratio of 7:1 at 145 °C for 2 h. The pulp was bleached using hydrogen peroxide (H2O2), and pulp properties (brightness, tear index and tensile index) of bleached and unbleached pulps were analyzed following the respective TAPPI standards. The produced black liquor was mixed with WH along with kitchen bio-wastes to produce compost. The properties of the compost were tested following the published protocols, i.e., wet digestion, Kjeldahl, vanadomolybdophosphoric acid, and Flame Spectrophotometry methods. Brightness, tensile index and tear index of bleached hand sheets were found to be 37.2%, 49.2 N m/g and 6.79 m.Nm2/g, respectively suggesting significant contribution of bleaching on WH paper quality. Addition of black liquor significantly increased the nitrogen and potassium content of bio-waste compost. Thus, WH can be used as a raw material for making handmade paper while the process by-product can be supplemented to improve the nutritional quality of compost. Such cottage-industry fabrication of WH green products could be developed to control the infestation of WH in water bodies, and this technology may provide for new possible sustainable livelihood option.

Integrating Compost and Biochar Towards Sustainable Soil Management

Composting of biowaste to organic fertiliser promotes resource recycling with various environmental co-benefits, including mitigation of nutrient loss, greenhouse gas emissions, and soil enrichment. As produced from the pyrolysis of organic waste, biochar could be added to compost for enhanced performances. The use of either compost or biochar or both has shown a positive effect on the overall soil quality, such as increasing soil pH and electrical conductivity, increasing soil organic matter, promoting soil carbon storage, and reducing the bioavailability of heavy metals. However, studies have reported contradictory observations and varying degree on the positive effect of such amendments on the aspects mentioned above. This review aims to evaluate the effect of biochar on composting towards a greener and cleaner process. The interacting mechanisms among biochar, compost and biochar-compost amendment upon soil application are discussed. The addition of biochar to compost effectively reduces nutrient loss and gaseous emission and promotes humification. The presence of biochar enrich specific groups of microbes that encourage nitrogen immobilisation. Biochar is more effective in improving the soil carbon pool, whereas compost has a more direct and persistent impact on the soil pH and cation exchange capacity. Upon applying mixed compost with biochar in soil, the organic amendments reduced heavy metals' bioavailability through the respective mechanisms. Different effects of compost and biochar on the soil properties and microbial community were observed, depending on the amendment type, soil condition and length of the application period.

Microplastics in soils: an environmental geotechnics perspective

Microplastics (MPs) are emerging persistent contaminants in the terrestrial subsurface, and evidence has emerged for significant effects of MPs on the biological and ecosystem functions of soils. Main MP sources include land spreading of sewage sludge and biowaste composts, plastic mulching film used in horticultural fields, waste water irrigation and leachate from the landfills, among others. This updated state-of-the-art review paper describes recent experimental and numerical research and developments in understanding the accumulation and fate and effects of MPs in the soil environment (focusing on their storage, degradation, transportation, leaching to groundwater etc.), followed by mitigation and bioremediation measures, including MP-eating soil bacteria and fungi and the best management practices for reducing MP pollution of soil. Other areas covered are the combined effects of MPs and various other environmental contaminants (heavy metals, organic pollutants and antibiotics) in soil ecosystems and the standardisation of methods for detection, quantification and characterisation of MPs in soils, which is critical for MP research. The paper concludes by identifying knowledge gaps and presents recommendations on prioritised research needs.

Effects of microorganism-mediated inoculants on humification processes and phosphorus dynamics during the aerobic composting of swine manure

There is significant interest in the treatment of swine manure, which is a hazardous biowaste and a source of pathogenic contamination. This work investigated the effects of microorganism-mediated inoculants (MMIs) on nutrient flows related to humification or phosphorus (P) dynamics during the aerobic composting of swine manure. The impact of MMIs on microbe succession was also evaluated. The addition of MMIs had positive effects associated with nutrient flows, including thermal activation, decreases in certain fluorescence emissions, lower mass loss and variations in levels of certain elements and functional groups. MMIs altered the maturation behavior and kinetics of organic matter while improving microbial activity. Phosphorus was found in the compost in the forms of MgNH4PO4·6H2O crystals and Poly-P as the IP species, and Mono-P as the OP species in compost generated from the dissolution or inter-transformation among P pools. These nutrient flows are attributed to changes in the structure of microbial communities as a consequence of introducing MMIs. Diverse microbial compositions were identified in different composting phases, although Bacillus appeared in each phase. This work provides support for the aerobic composting of hazardous biowaste as well as an improved understanding of nutrient flows, as a means of producing higher quality compost.

The Effect of Heat Removal during Thermophilic Phase on Energetic Aspects of Biowaste Composting Process

Composting is the natural, exothermic process where the huge amount of heat that is created is an issue of organic matter decomposition. However, too high temperature can reduce the microbial activity during the thermophilic composting phase. The aim of this study was to analyze the effect of heat excess removal from composted materials on the process dynamic. The experiment was performed in two parallel bioreactors. One of them was equipped with a heat removal system from the bed of the composted material. Three experiments were carried out with mixtures of different proportions: biological waste, wheat straw, and spent coffee grounds. The content of each option was determined based on a previous study of substrates to maintain the C/N ratio for the right composting process, provide adequate porosity composted material, and enable a proper degree of aeration. The study showed the possibility of receiving part of the heat from the bed of composted material during the thermophilic phase of the process without harm both to the course of composting and the quality of the final product. This shows that at a real scale, it can be possible to recover an important amount of heat from composted materials as a low-temperature heat source.

Fertilizing effect of human urine and ammonium nitrate as sources of nitrogen for sorghum [Sorghum bicolor (L.) Moench] under saline conditions

An experiment was conducted in a greenhouse to assess the influence of urine- and ammonium nitrate-N fertilization on sorghum biomass yield, shoot nutrient concentrations, and root:shoot ratio under different levels of NaCl salinity. Nitrogen applications were 90 and 180 mg N kg−1 soil substrate made from a mixture of bio-waste compost, quartz sand, and silty loam soil. A NaCl solution was added to the soil substrate to achieve target ECe of 1.3 (no salt added), 4.6, and 6.6 dS m−1, imitating different levels of salinity. Sorghum was sown as a second crop after maize, and biomass was harvested 12 weeks after sowing to assess dry weight and shoot nutrient concentrations. Salinity significantly decreased biomass yield regardless of N source. At an application rate of 90 mg N kg−1 substrate, biomass yield was 30% higher in plants fertilized with urine compared to ammonium nitrate regardless of salinity level. The application of 180 mg urine-N kg−1 raised substrate salinity and caused a significant decrease in shoot biomass yield in NaCl-treated substrates. Correlation analyses showed a relatively weak relationship between shoot N concentration and biomass yield in urine (r = 0.34; p > 0.05) compared to ammonium nitrate (r = 0.91, p < 0.0001). At a salinity of 6.6 dS m−1, nitrogen use efficiency was lower (33%) in urine compared to ammonium nitrate treatments. In conclusion, urine fertilization improves sorghum growth. However, where soil salinity is a problem (e.g. ECe 6.6 dS m−1), lower urine dosages should be considered.