Olena Stabnikova

Microbiological monitoring in the biodegradation of sewage sludge and food waste

Aim:  To study the microbiology of intensive, in‐vessel biodegradation of a mixture of sewage sludge and vegetable food waste.

Intensive aerobic bioconversion of sewage sludge and food waste into fertiliser

The aim of this research was to verify the possibility of recovering the nutrients present in sewage sludge and vegetable food waste as fertiliser after aerobic thermophilic intensive bioconversion. The process was performed in a closed reactor under controlled conditions of aeration, stirring and pH, at a temperature of 60°C, after addition of a starter bacterial culture of Bacillus thermoamylovorans SW25. End product with the best fertilising properties was obtained when sewage sludge, mixed with food waste, CaCO3 and an artificial bulking agent was thermally pre-treated. The content of volatile solids and organic carbon decreased from 82.8% to 62.3% and from 37.7% to 32.5% of total solids (TS) respectively, during 12 days of biocon-version. The stable organic fertiliser produced was a powder with moisture content of 5%. Furthermore, 3.4% of nitrogen, 0.4% of phosphorus and 2.9% of potassium were also present. Addition of 10-15g of this fertiliser to 1 kg of poor fertility soil increased the growth of different plants by 113-164%.

Intensive bioconversion of sewage sludge and food waste by Bacillus thermoamylovorans

The main aim of this work was to intensify conventional composting of a mixture of sewage sludge and solid food wastes by a one-stage thermophilic bioconversion of these wastes into an organic fertilizer. An intensive process was carried out in a closed system, with or without addition of a starter culture of Bacillus thermoamylovorans. The most effective thermophilic bioconversion of the mixture of food waste and sewage sludge, with addition of starter culture, was when the pH was buffered with calcium carbonate, or the pH drop in the material was prevented by preliminary removal of sulphides from sewage sludge by hydrogen peroxide.

Biotechnology for aerobic conversion of food waste into organic fertilizer.

A biotechnology for aerobic conversion of food waste into organic fertilizer under controlled aeration, stirring, pH and temperature at 55–65°C, is proposed. To maintain neutral pH at the beginning of the bioconversion 5% CaCO 3 was added to the total solids of the food waste. The addition of 20% horticultural waste compost as a bulking agent to the food wastes (w.w./w.w.), improved the bioconversion and increased the stability of the final product. No starter culture was needed for aerobic bioconversion of food waste into organic fertilizer for 10 days. The low contents of heavy metals in the raw materials used in the bioconversions ensured the safety of fertilizer from food waste for application in agriculture. The addition of 4% organic fertilizer to the subsoil increased the yield and growth of Ipomoea aquatica(Kang Kong) by 1.5 to 2 times. The addition of phosphorus is required to enhance the positive effect of organic fertilizer on plant growth.

Value-Added Biotechnological Products from Organic Wastes

Different organic wastes may be used as raw material for value-added products. The chapter represents organic wastes as a raw material for biotechnological transformation and gives brief descriptions of biotechnologies for transformation of organic wastes into such value-added products as enzymes, organic acids, flavours, polysaccharides, mushrooms, biodegradable plastics, animal feed, biomass for bioremediation, dietary fibers, pharmaceuticals, gibberellic acid, chemicals (acetone and butanol, glycerol) and fuel (ethanol and hydrogen). It describes microorganisms, which can be used for biosynthesis of value-added products, and highlights most essential factors affecting the process of their biosynthesis. Examples of biotechnologies for biotransformation of organic wastes into value-added products are presented. Such environmental biotechnologies as bioconversion of organic waste into compost or fertilizer, recovery of metals from solid and liquid wastes, recovery of phosphate and ammonium from liquid wastes by application of iron-reducing and iron-oxidizing bacteria are described in the chapter.

Removal of ammonia in a modified two-phase food waste anaerobic digestion system coupled with an aerated submerged biofilter:

Anaerobic digestion of food waste can reduce its volume, generate fuel biogas containing methane, and produce solid organic residue that can be used as a soil conditioner or fertiliser. Anaerobic digestion is more promising food waste disposal method than incineration and landfilling. The hybrid anaerobic solid-liquid (HASL) system, enhanced with a submerged biofilter for ammonia removal, was proposed for food waste digestion. Application of the submerged biofilter in the HASL system operated in batch mode increased concentrations of dissolved COD and volatile fatty acids in an acidogenic reactor, and total COD removal and methane production in a methanogenic reactor. The gas production in the enhanced HASL system was 86 l while in the conventional HASL system it was 54 l after 14 days of batch process. Methane production in the enhanced HASL system was increased by 26% in comparison with the conventional HASL system.