Decentralised Waste Water Purification

Germany is currently assuming a pioneering position in decentralised wastewater treatment in Europe, if not even in the world.

The amendment of the Waste Water Ordinance (AbwV) of 2 July 2002, which also set runoff concentrations for small-scale sewage treatment plants, the amendment of DIN 4261, as well as rising disposal costs and environmental impacts require intensive research activities in the field of decentralised wastewater treatment in future, too.

Decentralised methods for the treatment of waste water, and in particular small-scale sewage treatment plants, were long held to be inadequate within the meaning of modern waste water purification due to their poor performance capability. However, realistic comparisons of the costs and performance of modern decentralised waste water purification, national research projects and the pressure created by a number of interest groups have led to a change in attitude in many federal states. We have taken on the task of devising new methods of treatment in research and study projects, and to implement these in agricultural practice. Due to its specific composition of organic constituents, agricultural production wastewater is often deemed to be hazardous material, and can lead to the overburdening of municipal wastewater treatment plants.

Due to its specific composition of organic constituents, agricultural production wastewater is often deemed to be hazardous material, and can lead to the overburdening of municipal wastewater treatment plants.

The natural self-purifying capacity of water bodies is exploited in biological wastewater treatment systems. If waste water, regardless of its composition and concentration, is fed into a body of water, the very biocoenosis of organisms ideal for degrading the pollutants is developed after a certain length of time.

The micro-organisms involved are of crucial importance in converting this self-purification process into a technical process. These micro-organisms and the demands they place on their environment have dictated to a great extent the design of technical solutions for wastewater treatment. For this reason, systems were developed modelled on nature. The effect of the trickling filter process or of fixed-bed plants is predominantly based on the purifying capacity of the biofilm – a biocoenosis of various micro-organisms – growing on the different support materials. This method is particularly advantageous when, as is usually the case with decentralised plants, hydraulic shock loads must be assumed. Biofilms have large surfaces to adsorb and degrade the substances in the wastewater. The nature of sequencing batch reactor plants, also called SBR plants, is that biological reactions and the sedimentation of the activated sludge take place in one single reactor room. This is the best way to satisfy the special demand of membrane technology – saving space for secondary sedimentation.

In recent years, our research has focused particularly on planted soil filters and plant-based purification systems. Extensive research activities have shown that, in combination with appropriate primary treatment, these simple, cost-effective methods are highly suited to the purification of organically highly loaded wastewater, such as that which occurs in wine-making. With an average influent load of 1600 mg/l BSB 5, an effluent concentration of 4 mg/l BSB 5 could be proven, i.e. an over 99% elimination capacity.