Community composting strategies for biowaste treatment: methodology, bulking agent and compost quality.

The European Union's commitment to increase recycling and recovery rates of municipal solid waste requires significant changes in current waste management. Local governments are developing various strategies for treating the organic fraction of municipal waste (biowaste) via composting. Community composting centres (CCC), green waste collection, treatment points and community gardens are some of these new approaches. Population density and spatial distribution, together with the existence of community green areas, determine the location of the various infrastructures for recycling local biowaste. The composting process consumes high amounts of bulking agent (BA) necessary to provide the structure that allows, amongst other uses, biowaste aeration and microbial surface colonisation. Shredded green waste from parks, gardens and households can be used as BA in community composting and home composting. In this study, a total of 46 compost samples obtained from CCC with two types of handling were analysed: 22 samples treated by vertical flow (VF) and 24 samples treated by horizontal flow (HF). The HF model allowed better use of the volume of modular composting units and the VF model required less effort and time for the CCC operator. Mature, stable and high-nutrient-content composts were obtained with both models. These composts met the legal requirements to be used as an organic amendment, and they can be delivered to the participants or used in community gardens in the municipality.

Thermophilic composting of hydrocarbon residue with sewage sludge and fish sludge as cosubstrates: Microbial changes and TPH reduction.

The hydrocarbon residue in petroleum product storage tanks is waste generated in large quantities that must be properly managed to reduce its risk to the environment. By comparing the effect of two organic cosubstrates, the aim of our research is to determine the feasibility of composting as a bioremediation method for the treatment of the solid phase of the hydrocarbon residue. For this purpose, four treatments of the pollutant waste were established in triplicate: waste only; waste with bulking agent (1:2); waste with fish sludge and bulking agent (1:2:6); and waste with municipal sewage sludge and bulking agent (1:2:6). The composting system consisted of 12 reactors with a capacity of 30 L, each equipped with aeration and temperature control. Both at the beginning and the end of the experiment (20 days), we evaluated the physicochemical parameters, the structure of the microbial community through phospholipid fatty acid analysis, and the total petroleum hydrocarbon content (TPH). Treatments with cosubstrates maintained thermophilic temperatures, during 14 and 8 days in fish and municipal sludge respectively, while in the controls mesophilic conditions were maintained. The incorporation of fish sludge decreased TPH present in the initial mixture by 39.5%. The municipal sludge treatment resulted in a lower of temperatures and a TPH decrease close to 23.9%. In the control treatments, there was a slight TPH decrease, mainly due to the forced ventilation. Although, both composting treatments with cosubstrates proved adequate for the bioremediation of residue from hydrocarbon storage tanks, fish sludge presented best bioremediation conditions. Municipal sewage sludge provided a bioaugmentation effect due to its rich diversity and microbial biomass. Fish sludge could have biostimulant and surfactant effect producing an aliphatic mixture of pollutant waste with the nutritional requirements to promote the development of fungal communities.

Changes in microbial dynamics during vermicomposting of fresh and composted sewage sludge.

Municipal sewage sludge is a waste with high organic load generated in large quantities that can be treated by biodegradation techniques to reduce its risk to the environment. This research studies vermicomposting and vermicomposting after composting of sewage sludge with the earthworm specie Eisenia andrei. In order to determine the effect that earthworms cause on the microbial dynamics depending on the treatment, the structure and activity of the microbial community was assessed using phospholipid fatty acid analysis and enzyme activities, during 112days of vermicomposting of fresh and composted sewage sludge, with and without earthworms. The presence of earthworms significantly reduced microbial biomass and all microbial groups (Gram+ bacteria, Gram- bacteria and fungi), as well as cellulase and alkaline phosphatase activities. Combined composting-vermicomposting treatment showed a lesser development of earthworms, higher bacterial and fungal biomass than vermicomposting treatment and greater differences, compared with the control without earthworms, in cellulase, ß-glucosidase, alkaline and acid phosphatase. Both treatments were suitable for the stabilization of municipal sewage sludge and the combined composting-vermicomposting treatment can be a viable process for maturation of fresh compost.