An alternative to conventional sewage sludge composting technology can be vermicomposting, when manure worms are placed into the starting material, so the efficiency of breakdown and transformation of organic matter is increased by the activity of worms. Compared to conventional composting, higher-quality product can be produced with vermicomposting concerning agronomical value because of the properties of the finished material such as favourable particle size distribution, more easily available nutrients for plants and presence of plant growth stimulating compounds, high metabolic enzyme activity, better quality humic acid and humic substance content. In addition, worms are able to extract certain inorganic contaminants and accumulate them in their bodies, as well as to promote the breakdown of organic pollutants.
Hungarian Government Decree 50/2001 (IV. 3.) on rules of agricultural use and treatment of sewage and sewage sludge is the current Hungarian legislation, which relates to the utilization of materials in waste status. The regulation aims to avoid harmful effects on soils, surface and ground waters as well as on human health, on plants and animals due to the professional utilization of some sewage, sewage sludge and sewage sludge composts on agricultural areas. If toxic substances of the treated sewage sludge/sewage sludge compost do not exceed the limits specified by Ministry of Agriculture and Rural Development Decree 36/2006. (V. 18.) and the product meets the quality requirements, then it can be qualified to yield enhancing substance.
Municipal sewage sludge from Érd has very high TPH content (5000-6000 mg/kg), which inhibits agricultural utilization even according to Decree 50/2001. (IV. 3.) (TPH limit value: 4000 mg/kg). Based on the Decree 36/2006. (V. 18.) the exceedance of Cu limit is 3-fold (Cu limit value is 100 mg/kg) and for TPH it is 50-fold (TPH limit value is 100 mg/kg). Based on previous experiments, treatment of municipal sewage sludge from Érd solely by vermicomposting has not proved to be effective enough mainly due to the high TPH content of the sludge, despite the positive attributes of the produced material.
The main objective of this current project is the development of vermicomposting technology of sewage sludge, which is based on the foundations of conventional composting. The point of the development is that the fast “breakdown” stage of conventional sewage sludge composting takes place before the beginning of vermicomposting, but after that the “conversion” process is carried out by worms. A special additional technological element is the use of a vaccine which intensifies hydrocarbon degradation. The objective is to determine the necessary technological steps and optimum conditions for the process in order to prepare good quality organic material for agriculture, taking into account both agronomic and environmental aspects.
The technology development is achieved through small-scale and semi industrial experiments in prisms examining several factors, while the impact of the highest quality vermicompost will be studied on less favoured soils of Hungary and Norway in pot experiments under laboratory conditions. Expected outcome of the project is the development of a viable technology, which allows the production of a better quality material compared to dewatered sewage sludge and conventional compost, which as a product can also get out of waste status. This technology can greatly promote the recycling of sewage sludge, which is a very significant problem not only in Hungary but also in the European Union.
Without the support of the Green Industry Innovation project, sewage sludge from Érd would not be suitable for agricultural utilization (50/2001. (IV. 3.) Government Decree) even after vermicomposting. The consortium, formed for the implementation of the R & D project, has all the experience (research, project management, engineering, project implementation, financial), which makes it suitable for the successful implementation of the project. Furthermore, the plant in Érd, selected for the location of the project, has the facilities, infrastructure and investor supports by which the developed technological solutions can be fully applied, and the results of the R & D project can be incorporated into a factory scale sewage sludge treatment technology, which would result in the transformation of sewage sludge suitable only for deposition into a useable manure and soil amendment. The importance of the latter is also given by the fact that more than 15% of soils in agricultural areas of Hungary are currently classified as less favoured. Due to site conditions in the vicinity of Érd, raw materials to be included in the experimentation are available and potential users (farmers, growers) are accessible which are determining factors in terms of business plan and sustainability of the project.