The microbiological destruction of thiocyanate in activated sludge plants treating coke oven effluent

The treatment of effluents produced during the manufacture of metallurgical coke is normally carried out using the activated sludge process. The efficiency of activated sludges in purifying coke oven effluent depends largely on the maintenance of species of micro-organisms which destroy thiocyanate. The composition, production, toxicity and treatment of coke oven effluent at Corby steelworks are described. A review is presented which follows the progress made towards identifying and monitoring the species of bacteria which destroy thiocyanate in biological treatment plants purifying coke oven effluents. In the present study a search for bacteria capable of destroying thiocyanate led to the isolation of a species of bacteria, identified as Pseudomonas putida, which destroyed thiocyanate in the presence of succinate; this species had not previously been reported to use thiocyanate. Washed cell suspensions of P. putida destroyed phenol and thiocyanate simultaneously and thiocyanate destruction was not suppressed by pyridine, aniline or catechol at the highest concentrations normally encountered in coke oven effluent. The isolate has been included, as N.C.I.B. 11198, in the National Collection of Industrial Bacteria, Torrey Research Station, Aberdeen. Three other isolates, identified as Achromobacter sp., Thiobacillus thioparus and T. denitrificans, were also confirmed to destroy thi.ocyanate. A technique has been developed for monitoring populations of different species of bacteria in activated sludges. Application of this technique to laboratory scale and full scale treatment plants at Corby showed that thiobacilli were usually not detected; thiobacilli were el~inated during the commissioning period of the full scale plant. However experiments using a laboratory scale plant indicated that during a period of three weeks an increase in the numbers of thiobacilli might have contributed to an improvement in plant performance. Factors which might have facilitated the development of thiobacilli are discussed. Large numbers of fluorescent pseudomonads capable of using thiocyanate were sometimes detected in the laboratory scale plant. The possibility is considered that catechol or other organic compounds in the feed-liquor might have stimulated fluorescent pseudmonads. Experiments using the laboratory scale plant confirmed that deteriorations in the efficiency of thiocyanate destruction were sometimes caused by bulking sludges, due to the excessive growth of fungal floes. Increased dilution of the coke oven effluent was a successful remedy to this difficulty. The optimum operating conditions recommended by the manufacturer of the full scale activated sludge plant at Corby are assessed and the role of bacterial monitoring in a programme of regular monitoring tests is discussed in relation to the operation of activated sludge plants treating coke oven effluents.

A dynamic model for the activated sludge treatment of coke oven effluents

This is an Inter-Disciplinary Higher Degree (IHD) thesis about Water Pollution Control in the Iron and Steel Industry. After examining the compositions, and various treatment methods, for the major effluent streams from a typical Integrated Iron and Steel works, it was decided to concentrate investigative work on the activated-sludge treatment of coke-oven effluents. A mathematical model of this process was developed in an attempt to provide a tool for plant management that would enable improved performance, and enhanced control of Works Units. The model differs from conventional models in that allowance is made for the presence of two genera of microorganisms, each of which utilises a particular type of substrate as its energy source. Allowance is also made for the inhibitive effect of phenol on thiocyanate biodegradation, and for the self-toxicity of the bacteria when present in a high substrate concentration environment. The enumeration of the kinetic characteristics of the two groups of micro-organisms was shown to be of major importance. Laboratory experiments were instigated in an attempt to determine accurate values of these coefficients. The use of the Suspended Solids concentration was found to be too insensitive a measure of viable active mass. Other measures were investigated, and Adenosine Triphosphate concentration was chosen as the most effective measure of bacterial populations. Using this measure, a model was developed for phenol biodegradation from experimental results which implicated the possibility of storage of substate prior to metabolism. A model for thiocyanate biodegradation was also developed, although the experimental results indicate that much work is still required in this area.