Optimising mixed aerobic and anaerobic composting process parameters for reducing bacterial pathogenicity in compost-derived products

Assessment of the combined response of heavy metals and human pathogens to different additives during composting of black soldier fly manure

The bioconversion of black soldier fly (BSF) is a new model of livestock manure resourcing. However, the biochemical properties of BSF manure are unstable and direct application can be harmful to crops. Therefore, the effect of additives (biochar, humic acid and tea residue) on the removal of heavy metals and pathogens from BSF compost was investigated. Biochar inhibited the availability of Zn (58.9 %) and As (51.7 %) more significantly. Humic acid and tea residue significantly reduced the availability of Zn (60.8 %) and As (42.5 %) respectively. Humic acid and tea residue inhibited the bioavailability index of heavy metals more than biochar. At the end of composting, the total number of pathogenic bacteria was reduced by 80.1-96.0 % and pathogenic fungi by 41.4-99.9 %. Humic acid and biochar are more helpful in inhibiting the growth of pathogens. The abundance of dominant pathogenic genera was reduced by additive modulation. OM, EC, and temperature were the most key factors affecting the pathogenic bacteria. OM, pH, EC, Cu, Zn, and Cr also responded significantly to the pathogenic fungi. This study promotes the efficient conversion of livestock manure via BSF and provided theoretical guidance for the removal of pollutants in compost.

Effects of biochar and volcanic rock addition on humification and microbial community during aerobic composting of cow manure

Additives are important for accelerating humification during aerobic composting. The impacts of porous additives biochar and volcanic rock on the physicochemical parameters, maturity indicators, microbial communities, and bacterial functional metabolism during the aerobic composting of cow manure were investigated in this study. The results showed that the biochar addition decreased the E4/E6 value by 10.42% and increased the abundance of Geobacillus (1.69 times), and volcanic rock addition decreased the E4/E6 value by 11.31% and increased the abundance of Thermobacillus (1.29 times) and Paenibacillus (1.72 times). The network analysis demonstrated that biochar promoted maturity by reducing the abundance of Pseudomonas and increasing the abundance of genes related to the metabolism of other amino acids, while volcanic rock promoted maturity by reducing the abundance of genes related to nucleotide metabolism. These results provided data and theoretical justification for the selection of porous additives for composting.

Effect of the addition of biochar and wood vinegar on the morphology of heavy metals in composts

In the experiment, the morphology of heavy metals (Pb, Cr, Cd, and Ni, HMs) was characterized using flame atomic absorption spectroscopy. In addition, Fourier transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) were used to characterize the correlation between environmental factors and metal morphology in the rotting compost from several angles. The results showed that the humus treated with wood vinegar solution had a high degree of humification and rich aromatic structure. FTIR spectroscopy confirmed that the degree of humus aromatization gradually increased during the composting process, which enhanced the complexation of humus (HS) with HMs but had less effect on Ni. In addition, the optimum concentration of wood vinegar (WV) was determined to be 1.75%. The results of the study showed that in the Pb passivation treatment group, the proportion of soluble (Red) and exchangeable states (Exc) converted to oxidized (Oxi) and residual states (Res) was 8%, 14%, 6%, 1%, and 12% in the CK, T1, T2, T3, and T4 treatment groups, respectively; in the Cr passivation treatment group, the proportion of Cr-Red and Cr-Exc converted to oxidized and residual states was 31%, 33%, 25%, 29%, and 25%; in the Cd passivation treatment group, the proportions of Cd-Red and Cd-Exc converted to oxidized and residual states were 5%, 15%, 4%, 9%, and 11%, respectively; whereas the Ni treatment group did not show any significant passivation effect. The proportion of Pb-Oxi was relatively stable, Cr-Oxi was converted to Cr-Res, whereas Cd showed the conversion of Cd-Oxi to Cd-Exc. SUVA254 and SUVA280 showed significant positive correlations with Pb-Res, Cr-Res and Ni-Res, and significant positive correlations with moisture content (MC); whereas MC was significantly negatively correlated with each form of HMs. Total potassium (TK), total nitrogen (TN), and both carbon (TOC) were negatively correlated with Pb-Res and Pb-Exc. Structural equation modeling verified the relationship between environmental factors and HMs, and the composting results showed that the addition of biochar (BC) and a higher percentage of WV could increase compost decomposition and passivate HMs to improve its agronomic function.

Evaluation of different composting systems on an industrial scale as a contribution to the circular economy and its impact on human health

Due to the production of volatile organic compounds (VOCs), large-scale composting can cause air pollution and occupational health issues. Due to this, it is necessary to determine if the amount generated poses a health risk to plant workers, which can be a starting point for those in charge of composting plant facilities. As a result, the goal of this work is to conduct a thorough analysis of both the physicochemical features and the VOC generation of three large-scale systems. For ten weeks, the three different composting plants were monitored weekly, and VOC identification and quantification were performed using GC-MS gas chromatography. It has been observed that the biggest risk related with VOC formation occurs between the fourth and fifth weeks, when microbial activity is at its peak. Similarly, it has been demonstrated that xylenes and toluene are the ones that are produced in the greatest quantity. Finally, after ten weeks of processing, it was discovered that the material obtained complies with the regulations for the sale of an amendment.Implications: The evaluation and monitoring of the composting processes at an industrial scale is very important, due to the implications they bring. VOCs are produced by the operation of composting facilities with substantial amounts of solid waste, such as the companies in this study. These may pose a health risk to those working in the plants; thus, it is critical to understand where the VOCs occur in the process in order to maintain workers' occupational health measures. This form of evaluation is rare or nonexistent in Colombia, which is why conducting this type of study is critical, as it will provide crucial input into determining when the highest levels of VOC generation occur. These are the ones that may pose a risk at some point, but with proper occupational safety planning, said risk may be avoided. This work has evaluated three composting systems, with different types of waste and mixtures. According to reports, while composting systems continue to produce VOCs and their generation is unavoidable, the potential risk exists only within the plant. These findings can pave the way for the implementation of public policies that will improve the design and operation of composting plants. There is no specific legislation in Colombia for the design and execution of this sort of technology, which allows the use of organic waste.

Trends in the management of organic swine farm waste by composting: A systematic review

Pig farming contributes to the economic development of nations and supplies human food demand; however, it generates a large amount of organic waste which, if not managed properly, becomes a risk to the environment and human and animal health. Considering the relevance of composting and its usefulness for the use of waste, this study aimed to determine the global trends in the management of composting manure, mortality and other organic waste produced on pig farms over the last five years (2017-2022). Systematic search involved four databases: ISI Web of Science, Scopus, Ebsco and Scielo. Of the total findings, 56 articles were included in the review, further classified into 14 categories for their respective analysis: co-substrates/additives, microbial communities, antibiotic resistance, heavy metals, polycyclic aromatic hydrocarbons, microbiological/parasitological quality, phytopathogens, nitrogen transformation, bioinoculants, comparison/combination with other waste management techniques, factors affecting composting, swine mortality and plant growth promotion/phytotoxicity. The review exemplified the importance of swine mortality composting as an alternative for organic matter management in pig farms, considering that the process also includes manure, vegetable waste and wood chips, among others. Controlled factors throughout the process are a requirement to obtain a stable product with physicochemical and microbiological quality that complies with national and international regulations and that will be useful and safe for application on crops, ensuring environmental, animal, and human health.

Valorisation of food waste for valuable by-products generation with economic assessment

This study assessed the techno-economic feasibility of a biorefinery for valuable by-products (mainly hydrogen, ethanol and fertilizer) generation from food waste. The plant was designed to be built in Zhejiang province (China) with a processing capacity of 100 t food waste per day. It was found that the total capital investment (TCI) and annual operation cost (AOC) of the plant were US$ 7625549 and US$ 2432290.7 year^-1, respectively. After the tax, US$ 3141867.6 year^-1 of net profit could be reached. The payback period (PBP) was 3.5 years at a 7% discount rate. The internal rate of return (IRR) and return on investment (ROI) were 45.54% and 43.88%, respectively. Shutdown condition could happen with the feed of food waste less than 7.84 t day^-1 (2587.2 t year^-1) for the plant. This work was beneficial for attracting interests and even investment for valuable by-products generation from food waste in large scale.

Comparative evaluation of advanced oxidation processes (AOPs) for reducing SARS-CoV-2 viral load from campus sewage water

Presence of SARS-CoV-2 in wastewater is a major concern as the wastewater meets rivers and other water bodies and is used by the population for various purposes. Hence it is very important to treat sewage water in an efficient manner in order to reduce the public health risk. In the present work, various advanced oxidation processes (AOPs) have been evaluated for disinfection of SARS-CoV-2 from sewage water collected from STP inlet of academic institutional residential. The sewage water was subjected to ten AOPs, which include Ozone (O3), Hydrodynamic cavitation (HC), Ultraviolet radiation (UV), and their hybrid combinations like HC/O3, HC/O3/H2O2, HC/H2O2, O3/UV, UV/H2O2, UV/H2O2/O3, and O3/H2O2 to reduce SARS-CoV-2 viral load. Further, AOP treated sewage water was subjected to total nucleic acid isolation followed by RT-qPCR for viral load estimation. The sewage water treatment techniques were evaluated based on their viral concentration-reducing efficiency. It was found that ozone and ozone-coupled hybrid AOPs showed the most promising result with more than 98 % SARS-CoV-2 viral load reducing efficiency from sewage water. Interestingly, the best six AOPs used in this study significantly reduced both the SARS-CoV-2 and PMMoV (faecal indicator) viral load and improved water quality in terms of increasing DO and decreasing TOC.

Full-Scale of a Compost Process Using Swine Manure, Human Feces, and Rice Straw as Feedstock

Regarding the composting of rural waste, numerous studies either addressed the composting of a single waste component or were conducted at a laboratory/pilot scale. However, far less is known about the mixed composting effect of multi-component rural waste on a large scale. Here, we examined nutrient transformation, maturity degree of decomposition, and succession of microbial communities in large-scale (1,000 kg mixed waste) compost of multi-component wastes previously optimized by response models. The results showed that multi-component compost can achieve the requirement of maturity and exhibit a higher nutritional value in actual compost. It is worth noting that the mixed compost effectively removed pathogenic fungi, in which almost no pathogenic fungi were detected, and only two pathogenic bacteria regrown in the cooling and maturation stages. Structural equation models revealed that the maturity (germination index and the ratio of ammonium to nitrate) of the product was directly influenced by compost properties (electrical conductivity, pH, total organic carbon, moisture, temperature, and total nitrogen) compared with enzymes (cellulase, urease, and polyphenol oxidase) and microbial communities. Moreover, higher contents of total phosphorus, nitrate-nitrogen, and total potassium were conducive to improving compost maturity, whereas relatively lower values of moisture and pH were more advantageous. In addition, compost properties manifested a remarkable indirect effect on maturity by affecting the fungal community (Penicillium and Mycothermus). Collectively, this evidence implies that mixed compost of multi-component rural waste is feasible, and its efficacy can be applied in practical applications. This study provides a solution for the comprehensive treatment and utilization of rural waste.