Biochemical sewage treatment.

Biochemical cleaning is one of the basic methods of the deep sewage treatment, allowing removing from them the various organic and some inorganic compounds. During biochemical cleaning the dissolved organic substances are subjected to biological disentigration by means of microorganism in the presence of oxygen (aerobic process) or in its absence (anaerobic process).

During biochemical cleaning the substances, contained in sewage, are not utilized, and they are processed into excess sludge which it is necessary to neutralize.

Activated sludge is a complicated complex of microorganisms of the various classes, the elementary microscopic worms, water plants.

When assimilating organic substances by microorganism the structure of compounds has essential value. Saturated compounds are biologically resistant and they may be assimilated only by some types of microorganisms. Nonsaturated organic compounds are good source of carbon for many microorganisms.

Depending on characteristics of sewage and the purpose of cleaning the technological scheme of biochemical sewage treatment are differentiated.

Biological oxidation is carried out both in natural conditions on fields of a filtration, irrigation and in biological ponds and in the artificial conditions in аerotanks and on the biofilters.

Aerotank is capacitive flow –type structure with freely floating activated sludge in the volume of treating water. For aerobic biochemical treatment, large amount of sewage is used.

Sectioning aerotanks are reinforced concrete reservoirs, divided into 4-10 section. From аerotanks the mixture of treated sewage is directed to the secondary settling tank, where activated sludge settles on the bottom of settling tank and then it is removed in the reservoir by means of disposal truck. Since during biological oxidation the growth of biomass takes place, its excess is removed from system and it is directed to the sludge site.

In biological filters, the activated biomass is fixed on a motionless material, and sewage flows around it’s by thin film layer. They are applied at the discharge of sewage to 20 - 30 000 m3/day.

According to type of the media material on which surface the biological oxidation of pollution proceeds, there are biofilters with volumetric and plane media. Volumetric media materials are gravel, crushed stone, expanded clay aggregate; plane are made from plastic, ceramics, metal, fabrics.

Not soluble pollution in water form the biological film, populated with organisms on a surface of the biofilter. During work of biofilters the film dies off, falls down and it is regenerated again. The cleaned water in the biofilter is chlorinated and directed to the secondary settling tank, where died film is delayed. In the filter the biogenic elements is added as salts of nitrogen and phosphorus. To increase concentration of pollution it is necessary to add the sewage.

In order to provide the life of microorganisms the sewage, supplying on the filter, should contain no more than 25 mg /l of oil products and no more than 1 g/l of the dissolved salts.

In biofilters with plane media the fixed blocks from sheet plastic with the advanced specific surface (90-110м²/m³) and a high share of free volume (93-96 %) are used as packing. Blocks can be performed from polyvinyl chloride, polystyrene, polyethylene, polypropylene and polyamide.

Methane tanks are constructions for anaerobic fermentation, working according to principle of reactors with full agitation. Typical methane tanks have useful volume of one tank 1000 - 8000 m³. This volume can be divided into 4 parts which have different functions: formation of floating crust, sludge water, fermentation, condensation and additional stabilization of sediment at storage (up to 60 days).

Tertiary treatment is applied to remove particles of activated sludge, biofilm, residual organic pollution, biogenic elements (N and P) and the bacterial pollution, contained in biologically cleaned sewage and complicating a reuse of sewage in systems of circulating water supply.

Дата добавления: 2015-10-26