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Recycling of waste from housing and communal services into secondary material resources based on the study of the qualitative composition of sewage sludge from Blagoveshchensk treatment facilities

The article considers the possibility of introducing low-waste technology as a method of production. It allows to have the most rational and integrated use of raw materials and energy in the cycle of raw resources, production, consumer and secondary resources, so that any impact on the environment does not disrupt its normal functioning. Intensification of agriculture and insufficient introduction of organic matter into the soil lead to a decrease in humus, which is the main fertilizer. Hence, there is an urgent need to maximize the production of all types of organic fertilizers, including non-traditional ones. Therefore, the priority aim in this field is to identify the possibility of using sewage sludge as a fertilizer to produce a good environmentally safe crop.


Introduction
Technology that allows getting a minimum of solid, liquid and gaseous waste is called a low-waste one and at the present stage of development of scientific and technological progress it is the most realistic one. The set of measures to reduce the amount of harmful waste to a minimum and decrease their impact on the environment includes development of various types of waste-free technological systems and water circulation cycles based on wastewater treatment; development of systems for processing industrial waste into secondary material resources; creation and release of new types of products taking into account the requirements of their re-use; creation of fundamentally new production processes that allow to eliminate or reduce the technological stages at which the waste is generated. Development of waste-free and low-waste technological processes is the most rational way to protect the environment from pollution, which significantly reduces the anthropogenic influence.
A rational system of water disposal and wastewater treatment is a necessary element of life support for every modern city. Sewage sludge (SS) is the main waste generated during the operation of treatment facilities. SS contains a wide range of various organic and inorganic substances of biogenic and abiogenic origin, including toxic elements (heavy metals, arsenic, fluorine, etc.), pathogenic microorganisms, petroleum products, etc. The bulk of SS isn't used for practical application and is stored in landfills, causing large-scale environmental pollution. The most rational approach to dealing with SS is to prevent (or minimize) their formation. This approach requires a radical restructuring of result, root growth occurs abnormally. Sandy and dusty soils are most affected by such structural changes. Adding organic fertilizers to such soils improves their quality, resulting in a higher crop than when applying the optimal amount of conventional fertilizers, but without adding organic matter (De Haan S., 1980). Sludge solids are more effective than equivalent amounts of farmyard manure (Epstein E., Taylor J., 1976; Gypta S., Dowdy V., 1977; Kladivko E., Helson D., 1979).
In Blagoveshchensk, several tons of sewage sludge (SS) are produced annually at treatment facilities (table 2), which is then taken for storage to specially prepared sites. Currently, these sites are almost all filled with SS, so there is a problem of further disposal. According to the results of SS studies after the mechanical dewatering shop in the waste water control laboratory of the testing center for water quality research of Amur municipal systems LLC, Blagoveshchensk, the qualitative composition of the sludge in Blagoveshchensk is the following: ash content 47.6 %, organic matter 52.4%, total phosphorus 13.35% (table 1, 2). The composition of the sludge also includes heavy metals such as: Cd, Cu, Zn, Cr, Pb, Ni. Cu -121.2 mg-kg/dry substances, Pb -13.4 mg-kg/dry substances, Zn -462.8 mg-kg/dry substances, Cd -1.21 mg-kg/dry substances, Cr-31.9 mg-kg/dry substances, Ni -36.11 mg-kg/dry substances (table 1).
The maximal allowable (MA) of heavy metals in SS as a fertilizer for agricultural crops is Cd<30 mg-kg/dry substances, Cu<1500 mg-kg/dry substances, Pb<1000 mg-kg/dry substances, Zn<4000 mgkg/dry substances, Cr<1200 mg-kg/dry substances, Ni<400 mg-kg/dry substances [8].  By reducing the intensity of accumulation, metals are placed in the next row: Cu, Cd, Pb, Ni, Zn. It was found out that the action of humic substances on Cu, Pb, Cr leads to the formation of chelated compounds and a decrease in the toxicity of these heavy metals.
Based on the above, it can be concluded that the sludge of Blagoveshchensk wastewater treatment plants is very diverse in its chemical composition. Heavy metals that are part of the sewage sludge of Blagoveshchensk do not exceed the maximal allowable (table 3).
As for organic matter, ash and phosphorus, their percentage content in the sludge is quite large, which increases the value of the sludge as a fertilizer and will have a favorable effect on the crop. The sludge obtained at the Blagoveshchensk treatment facilities has a high fertilizer value and can be used as a fertilizer for agricultural crops [9].

Conclusion.
The lack of effective methods of disposal of this type of waste in the world practice and the resulting aggravation of the environmental situation (pollution of the atmosphere and hydrosphere, rejection of land areas for landfills for SS storage) indicate the relevance of finding new approaches and technologies to involve SS in economics.
Currently, we have to deal with the problem of multi-tonnage waste generated annually at domestic and industrial wastewater treatment plants. According to research results, sewage sludge from the biological treatment plant of sewage treatment facilities in Blagoveshchensk has agrochemical