Respiration rate monitoring of Antwerp treatment works showed periods when the activated sludge was up to 40% inhibited, with resultant sludge washout episodes. Using the Health monitoring test, a pattern of ‘normal’ respiration rates for a plant can be determined. Lower respiration rates will alert the treatment works to a chronic toxicity problem, allowing corrective actions to be taken. Toxicity monitoring can now be carried out on a routine daily basis, at all treatment works receiving potentially toxic wastewaters. This is especially important if there has been a history of poor plant performance.
If industrial wastewater entering a treatment works contains toxic components the rate of biodegradation will be inhibited or stop completely. This can result in failed consents and will certainly give rise to operational problems. Visible indications include deflocculation, bulking and the appearance of filamentous bacteria. Sometimes, there are no visible effects. When the sludge bacteria are inhibited, there is the possibility of toxicity carryover in the effluent that is discharged to receiving waters. With new environmental legislation being introduced, worldwide, to protect the natural environment, toxin discharge is now a serious concern for treatment plant managers.
If toxicity is identified in a mixed sewage entering a treatment works, the problem for the plant manager is to track and identify the source of the toxicity. This can be done by sampling the effluent stream at various points in its length. By working in a logical sequence back up the sewer network the number of samples can be minimised. This type of testing should be rigorously enforced for new product introduction by a waste producer, as well as sampling the effluents directly at source. The samples would be tested against the activated sludge of the receiving works, using the Respiration Inhibition Test or the Nitrification Inhibition Test.
Federal and State regulatory agencies are increasingly requiring additional water quality testing and controls of the toxicity of discharges to receiving streams. Granular Activated Carbon (GAC) helps meet these pollution regulations. If organic chemicals have been identified as contributing to discharge toxicity, Calgon Carbon Corporation can work with facilities, and their engineering firms, to help meet stringent criteria associated with their NPDES permit. GAC can be employed as a cost-effective treatment for removal of organic compounds and toxicity. Even in situations where activated sludge treatment or powdered activated carbon is used for primary wastewater treatment, post treatment with GAC may be necessary to achieve toxicity compliance.
Water companies, water authorities or publicly-owned treatment works (POTW) need to have some knowledge of the composition of the wastes they it receive. In addition to testing for ammonia and BOD or COD levels, treatment works can license industrial discharges on the basis of concentrations of some of the known toxic compounds. However, it is recognised that very many non-regulated toxic materials still enter the treatment works and reduce the efficiency of biodegradation, and may cause toxic shock. The way is now open for more widespread use of direct toxicity tests as a basis for toxicity-based consents. Samples of the industrial effluent are collected at source, for testing on the actual bacteria of the receiving activated sludge. The tests used are the Respiration Inhibition Test and the Nitrification Inhibition Test. Note that this approach mirrors that of the regulators of discharges to receiving waters, who are now using direct toxicity tests (DTA) or whole effluent toxicity tests (WET tests) in order to protect the receiving environment.