Twenty-eight process wastewaters and thirty-seven organic substances identified in the wastewater of the Kashima petrochemical complex were subjected to biodegradability tests. The tests consisted of the activated sludge degradability method and a supplementary test using the respiration meter method. Both tests utilized the activated sludge of the Fukashiba industrial wastewater treatment plant, which was acclimatized to the wastewater and organic substances. The 28 process wastewaters were classified into biodegradable, less biodegradable, and non-biodegradable according to the percentage TOC removal and the BOD5/TOC ratio of the wastewater. The 37 organic substances were also classified into biodegradable, less biodegradable and non-biodegradable according to TOC and CODMn removal. In general, chlorinated compounds, nitro-aromatics and polymerized compounds were difficult to biodegrade. From the biodegradability tests of the factory wastewaters, it was found that the refractory CODMn loads of these factories contributed to the load remaining in the effluent of the wastewater treatment plant. Various improvements were made to reduce the discharge of refractory substances from the factories.

The Kashima petrochemical complex and the Fukashiba industrial wastewater treatment plant are described. The complex consists of 19 core factories (petroleum, petrochemicals, and thermal power generation) and 39 other factories (including organic chemicals, foods, metals, machinery, etc.). The total amount of industrial wastewater produced is 59,800 m3/day. The treatment plant also accepts municipal wastewater from the surrounding area, totalling 1,100 m3/d. A system for charging for the industrial wastewater has been introduced. The water quality standards for the industrial wastewater discharged to the sewerage system and the effluent of the treatment plant are described. The main treatment process is activated sludge with operational conditions of high dissolved oxygen and long solids retention time (SRT). These operational conditions solved the problems of high ammonia and refractory substances in the influent. Complete nitrification occurred under the low alkalinity conditions and the effluent COD was low due to the long SRT. Successful operation and maintenance were achieved by good co-operation between the factories and the treatment plant.