Anaerobic wastewater treatment

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The anaerobic wastewater treatment is to remove harmful or interfering organic carbon compounds by microbiological degradation processes, without the presence of oxygen ( anaerobic run). Bacteria gain the energy they need for their metabolism by converting the organic carbon compounds into organic acids and, subsequently, mainly into methane , carbon dioxide and hydrocarbons . Anaerobic wastewater treatment is a possible sub-process in sewage treatment plants .

Temperature ranges

In most cases, the wastewater needs to be heated to reach the temperature required for the bacteria. The temperature ranges are designated as follows:

  • Thermophilic : greater than 40 ° C, optimally 50 ° C to 57 ° C, increased gas yield, shorter required residence time, better settling of the sludge and increased germ destruction. However, operation is susceptible to temperature fluctuations.
  • Mesophile : 20 ° C to 40 ° C, optimally 35 ° C to 40 ° C, lower gas yield
  • Psychrophilic : less than 20 ° C, mostly without heating, compare anaerobic sludge stabilization in the "Emscherbrunnen", a sedimentation basin in which the sludge sinks under its own weight into a septic tank below the sedimentation area.

Lazy stages

The anaerobic digestion that takes place in digestion towers is basically divided into 4 stages:

  1. Hydrolysis phase: splitting of carbohydrates, fats and proteins into their fragments and polymeric substances.
  2. Acidification phase: acidification to H 2 , CO 2 , organic acids, acetic acid and alcohols.
  3. Acetogenic phase: conversion to acetic acid and small amounts of methane.
  4. Methanogenic phase: Acetic acid is broken down by methane bacteria and methane is produced.

Advantages and disadvantages

The advantages of the procedure are:

  • No energy requirement for ventilation.
  • Extraction of methane , which can be used for heating or electricity generation. Desulfurization may be required.
  • Low excess sludge production.
  • Some chemical compounds that are not aerobically degradable can be broken down.

The disadvantages of the procedure are:

  • The achievable residual concentrations usually do not allow direct discharge into the receiving water . A further purification stage with aerobic processes is therefore necessary ( e.g. activated sludge process , trickling filters ).
  • The process is sensitive with regard to the condition of the inlet and compliance with the operating conditions (e.g. temperature, pH value). The process can be inhibited by ammonium, hydrogen sulfide, copper, zinc, lead, cadmium or mercury.

commitment

Anaerobic wastewater treatment is used for highly concentrated wastewater (food industry, agriculture, pulp industry, animal carcass disposal, chemical parks ).

Sludge concentrations of 20 to 50 g / l can be achieved in the anaerobic reactors. A sludge load of 0.2 to 0.3 g COD per g dry substance of the sludge in the reactor and per day can be assumed for the dimensioning . In order to break down one g of COD per day, 3 to 5 g of dry matter must be kept in the anaerobic reactor.

literature

  • Wolfgang Bischofsberger et al. (Ed.): Anaerobtechnik. 2nd completely revised edition. Springer Verlag, 2004, ISBN 3-540-06850-3 .