Biological assessment of waste and produced organic matter during metagenesis

Abstract

Background. Modern advances in biotechnology make it possible to industrialize the processing of organic waste, particularly that generated in livestock farming, and widely utilize it. Therefore, the purpose of this study was to bioecologically evaluate organic matter obtained by metagenesis for subsequent utilization. Materials and methods. Three types of biodegradable organic waste were used as test materials: chicken manure, cattle manure, and food waste with a moisture content of 85–95 %. Standard laboratory methods were used. Results. The study established that the pH of the waste environment is fundamental for the habitat of anaerobic microorganisms, the development of which determines the fermentation processes. Food waste consisted of products and had a pH in the acidic range of 5.5, cattle manure had a pH close to neutral (7.5), which is associated with a high content of organic acids, while chicken manure had a fairly high alkaline environment. The chemical composition of the waste before fermentation was shown: the dry matter content in chicken manure was 25 %, in cattle manure – 15 %, and in food waste – 40 %. The organic carbon content in food waste was 48, in chicken manure – 45, and in cattle manure – 35 % of dry matter. Food waste contained Ntotal – 2.8, in chicken manure – 4.5, and in cattle manure – 3.0 % of dry matter. The environment change in the setup during biochemical processes is demonstrated. It was found that the biogas yield over 15 days of fermentation was 12.0 ml/g dry matter for poultry manure, 20.0 ml/g dry matter for cattle manure, and 7 ml/g dry matter for food waste. During fermentation, the reaction of the environment in chicken manure increased to 7.8, while it decreased for cattle manure (7.2) and food waste (4.2). The processed waste showed a slight decrease in organic carbon and dry matter content, from 5 % to 15 %, with a low biogas yield. The total nitrogen content increased for all variants compared to the original waste due to the release of ammonia nitrogen during protein decomposition. The processed chicken manure was shown to have the highest total nitrogen content (5.0 %), which included the formed ammonia nitrogen. The high residual content of organic matter and nitrogen compounds in the processed waste allows it to be used as organic fertilizers. Conclusions. All wastes studied were biodegradable. They demonstrated low fermentation potential. During metagenesis, the reaction of the environment of the processed waste changes. With low biogas yields, the chemical composition of the resulting liquid organic matter was characterizedby a slight decrease in dry matter and organic carbon content (5–15 %). During organic matter mineralization, chicken manure had the highest total nitrogen content (5.0 %).