Process water is one of the most challenging for analysis instrumentation. Mostly this water is characterized by a certain purity, fluctuating loads, as well as very high salt concentrations. Since any disturbance in water-circuits can lead to an entire plant shutdown, resulting in huge costs, reliable and fast online water analyzers are an essential. Due to the diverse demands of various measurement challenges, application-specific analyzers provide huge advantages against standard analyzers that are used for every application.
In industrial manufacturing companies, before a new process comes on-line, it is important to measure the toxicity of the effluent stream. This is especially the case for companies who treat their own waste. From the toxicity value (EC50) obtained, it may be a cost-effective solution to simply discharge the effluent to the treatment works at a slow and defined rate to minimise damage to the activated sludge. Following a period of acclimatisation it is often possible to increase feed rates to the plant and this can again be managed using the Strathtox Respirometer. An alternative approach is to undertake toxicity reduction procedures, such as neutralisation or acid hydrolysis, in pilot-scale laboratory studies. The Respiration or the Nitrification Inhibition Test may be used for this. In the future, toxicity reduction may be stipulated by local authority, water company or publicly-owned treatment works prior to giving discharge consents. Toxicity reduction may be evaluated using toxicity tests on activated sludge provided by the treatment works.
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.
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.
Hydrogen peroxide (H2O2) has been used to reduce the BOD and COD of industrial wastewaters for many years. While the cost of removing BOD / COD through chemical oxidation with hydrogen peroxide is typically greater than that through physical or biological means, there are nonetheless specific situations which justify the use of hydrogen peroxide. These include: Predigestion of wastewaters which contain moderate to high levels of compounds that are toxic, inhibitory, or recalcitrant to biological treatment (e.g., pesticides, plasticizers, resins, coolants, and dyestuffs);
Pretreatment of high strength / low flow wastewaters – where biotreatment may not be practical – prior to discharge to a Publicly Owned Treatment Works (POTW);Enhanced separation of entrained organics by flotation and settling processes; and Supply of supplemental Dissolved Oxygen (DO) when biological treatment systems experience temporary overloads or equipment failure.