After a mechanical pre-treatment by a grid and aerated sand trap, raw sewage arrives into the buffer with variable water levels, where additionally to hydraulic equalisation a hydrolysis of ﬁne dispersed pollutants and ﬁrst biochemical conversion of organic pollutants into volatile fatty acids takes place. From here a constant quantity of acidiﬁed sewage is pumped into the anaerobic reactor, containing active methanogenic bacterial bioﬁlms, ﬁxed on adsorbing porous LEVAPOR-carrier , enabling a fast and quantitative microbial colonisation and retention of active cells in the reactor. In this reactor bioconversion of generated acetic acid intobiogas, takes place at ambient temperatures. The sludge growth in anaerobic process is only 3 to 5% of removed COD, instead of 35% in the aerobic treatment, resulting in a remarkably better process economy. Final treatment of residual pollutants occurs in a subsequent aerobic ﬂuidised bed bioﬁlm reactor, where additionally to COD removal, quantitative nitriﬁcation of ammoniacal nitrogen into nitrate (NO3-) takes place. Aerobically treated efﬂuent, containing suspended biomass leaves the reactor to the clariﬁer, where sludge ﬂocs will settle, while retention of LEVAPOR cubes with ﬁxed bioﬁlm occurs by a screen, installed inside of the reactor.
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