Biodegradation of naphthalenesulphonic acid-containing sewages in a two-stage treatment plant

The production of naphthol the coupling compound in the syntheses of azo-dyes occurs a naphthalenesulphonic acid-containing wastewater. The aerobic biodegradation of a complex mixture of naphthalenemono- and -disulphonic acids with high amounts of inorganic salts was examined in a two-stage plant with specially adapted and immobilized microorganisms fixed on broken sand particles. The plant consists of two airlift-loop reactors. An interposed settling tank separates the two different bacterial communities in the stages. In the first stage the sequential metabolization of naphthalene-2- and-1-sulphonic acid was achieved by strain Pseudomonas testosteroni A3 at residence times down to 1.5 h. The total degradation of remaining naphthalene-1-sulphonic acid and the degradation of recalcitrant naphthalenedisulphonic acids was obtained by a defined mixed culture in the second unit. Because of the more recalcitrant character of the remaining components in the second stage examinations with Na2SO4-loaded and salt-free wastewater were carried out at mean residence times between 50 and 6.3 h. With salt-loaded sewage an overall degradation of approximately 71% was achieved. The main component in the effluent was non-biodegradable naphthalene-1.5-disulphonic acid. Investigations with salt-free wastewater have shown an increasing overall degradation up to 84%. Thus, in the presence of inorganic salts a considerable inhibition of the biological degradation of the recalcitrant substances in the second unit was found.