Changes in the ecological properties of organic wastes during their biological treatment

Evaluation of the Use of Sewage Sludge Biochar as a Soil Amendment—A Review

In recent decades, minimization and recycling/reuse policies were introduced to reduce the quantities of generated waste and for alternative waste recovery. Organic wastes represent 46% of total global solid waste. Possible uses of organic wastes include using it as fertilizer and amendment for soil, for energy recovery and for the production of chemical substances. Sewage sludge disposal and reuse are identified as future problems concerning waste. The total amount of sludge generated in the entire world has increased dramatically, and this tendency is expected to increase significantly in the years to come. In most developed countries, special attention is given to sewage sludge treatment in order to improve the quality and safety of using it on the ground surface. Sewage sludge pyrolysis is considered an acceptable method, from an economic and ecological perspective, for the beneficial reuse of sewage sludge. This method has many advantages because, during the pyrolysis process, the sludge volume is reduced by 80%, pathogenic agents and hazardous compounds from sewage sludge are eliminated, metals are immobilized in solid residue and organic and inorganic fractions are immobilized in a stabilized form of pyrolytic residues (biochar). The biochar generated by sewage sludge pyrolysis does not contain pathogenic agents and is rich in carbon and nutrients.

Assessment of the Effect of Solid Waste Dump Site on Surrounding Soil and River Water Quality in Tepi Town, Southwest Ethiopia

An increase in urban population and the rising demand for food and other essentials perpetuate a rise in the amount of waste being generated daily by each household. In Ethiopia, this waste is eventually thrown into open dump sites. It can cause severe impact on soil and surface water quality. As a result, it becomes the probable source of human health risk through food chain. Therefore, this study was aimed at assessing the effect of a solid waste dump site on surrounding soil and river water quality in Tepi town, Southwest Ethiopia. Three surface water, one leachate, and four soil samples were collected and analyzed. Six heavy metals for surface water and leachate samples and four heavy metals for soil samples were measured by flame atomic absorption spectroscopy. In addition, physiochemical parameters were analyzed using standard methods. The data were analyzed statistically using Origin pro version 8.0 computer software packages. The pH of soil was slightly basic ranging from 8 ± 0.1 to 8.7 ± 0.21. Electrical conductivity was lower at 60 meters (1800 ± 0.5 μs/cm) and higher in the other sample sites (3490 ± 0.66-4920 ± 1.04 μs/cm). The concentration of heavy metals in soil samples revealed cadmium (0.53 ± 0.01-2.26 ± 0.02 mg/kg), zinc (623.93 ± 0.29-859.41 ± 0.02 mg/kg), lead (3.26 ± 0.25-57.560.26 mg/kg), and copper (204.06 ± 0.06-337.11 ± 0.01 mg/kg). Lead, cadmium, manganese, nickel, copper, and zinc were found in the leachate water; nickel and manganese were found in the nearby river water; BOD₅ and COD for both leachate and stream water samples were found to be higher than standard guideline values. The finding suggested that solid waste open dump site adversely affects soil and water quality in the study area and becomes a probable source of risk for human health via the food chain.

Fungal and bacterial successions in the process of co-composting of organic wastes as revealed by 454 pyrosequencing

Composting is viewed as one of the primary methods to treat organic wastes. Co-composting may improve the efficiency of this treatment by establishing the most suitable conditions for decomposers than those present in the individual wastes. Given that bacteria and fungi are the driving agents of composting, information about the composition of their communities and dynamics during composting may improve reproducibility, performance and quality of the final compost as well as help to evaluate the potential human health risk and the choice of the most appropriate application procedure. In this study, the co-composting of mixtures containing two similar components (organic fraction of municipal solid waste and sawdust polluted by oil) and one discriminate component (sewage sludges of different origin) were investigated. Bacterial and fungal community successions in the two mixtures were analyzed during the composting process by determining the change in their structural dynamics using qPCR and 454 pyrosequencing methods in a lab experiment for a period of 270 days. During the initial composting stage, the number of 16S bacterial copies was (3.0±0.2) x 10⁶ and (0.4±0.0) x 10⁷ g^-1, and the Rhodospiralles and Lactobacialles orders dominated. Fungal communities had (2.9±0.0) x10⁵ and (6.1±0.2) x10⁵ ITS copies g^-1, and the Saccharomycetales order dominated. At the end of the thermophilic stage on the 30^th day of composting, bacterial and fungal communities underwent significant changes: dominants changed and their relative abundance decreased. Typical compost residents included Flavobacteriales, Chitinophagaceae and Bacterioidetes for bacteria and Microascaceae, Dothideomycetes, Eurotiomycetes, Sordariomycetes, and Agaricomycetes for fungi. During the later composting stages, the dominating taxa of both bacterial and fungal communities remained, while their relative abundance decreased. In accordance with the change in the dominating OTUs, it was concluded that the dynamics of the bacterial and fungal communities were not similar. Analysis by non-metric multidimensional scaling (NMDS) revealed that the bacterial communities of the two composts became progressively more similar; a similar trend was followed by the fungal community.