Water & Wastewater Treatment Magazine
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10 | OCTOBER 2017 | WWT | www.wwtonline.co.uk The Talk: opinion tari s. The only question is whether we support the principle of a national cost of providing service, or if we prefer the current rather arbitrary regional boundaries. To go with a standard tari based on a national cost of providing service there should then also be a national level of service. This of course is almost impossible to deliver with conventional hard measures of service. Every street in the country gets a di erent level of wholesale service depending on the details of the local water and wastewater systems. But if service was measured not as the lack of failures, but rather as the compensation paid when failure occurs, then an equitable system is possible. A national level of compensation could be de• ned based on a national survey carried out by, or on behalf of, the retailers. Rather than asking customers, "how much extra would you pay so that someone else isn't • ooded", they would be asked, "if someone is • ooded, how much compensation should they get." Most customers would understand that. When there is a failure of service a ecting customers, the retailers pay the standard compensation to the customers and reclaim it from the wholesalers. Ofwat would need to monitor that retailers were paying their customers the compensation, but this is a similar role to their current one in monitoring GSS payments. Retailers should ensure that wholesalers pay them the standard compensation. This then, has one of the real characteristics of a market where price and cost signals drive real levels of service provided by the wholesalers. If they are at risk of paying large amounts of compensation in an area, they will invest in the system to improve performance and avoid the payments. With service de• ned as compensation for failure, the door is also open to each individual householder to have an individual level of service. They can opt to pay a higher charge to the retailer, and in return, when something goes wrong, the retailer pays them higher compensation. It is the retailer's calculation as to how much extra they should charge customers to provide the extra compensation. It would drive improvements, since if a retailer has many customers in an area prepared to pay more for a higher level of compensation, then it becomes worthwhile for that retailer to fund the wholesaler to improve the real level of service to their customers and others in that area. So the introduction of competition could be the trigger to put right a lot of what is currently wrong with charging for water services and give us a system that aligned with principles that we could support. The question remains - are we ready to make such a radical change? SPONSORED BY DR JOHN LEAR TECHNICAL DIRECTOR BIOLOGICAL PREPARATIONS LTD Nutrient imbalance in wastewater Keeping carbon, nitrogen and phosphorus in the right ratio can be a challenge at wastewater plants, but help is at hand W e have seen how the addition of suitable microbial strains can enhance activity, increase degradation of recalcitrant contaminants and reduce odours in the wastewater treatment plant, and that ensuring suit- able conditions in terms of temperature, pH and aeration will optimise activity. However further modi• cation of condi- tions may be required, for example to rectify nutrient imbalances or to manage the growth of • lamentous organisms. Nutrient balance is an important issue, as microbes require a particular nutrient ratio in order to carry out their activities at optimum eŠ ciency. Carbon, nitrogen and phosphorous are the most important of these nutrients and C:N:P ratios between 100:5:1 and 100:10:1 should be maintained in order to ensure maximum microbial activity in aerobic wastewater treatment. A number of trace elements or micronutrients are also required. O" en such conditions will be naturally maintained within the wastewater treatment plant but this by no means goes without saying. Nitrogen for example, essential to bacteria for the synthesis of amino acids and nucleic acid bases, may be in excess in wastewaters from dairy or meat processing facilities yet de• cient in certain industrial e• uents. If the C:N:P ratio is not correct, microbial growth can be signi• cantly limited and eŠ ciency of the plant greatly reduced, risking high outlet BOD, COD and TSS levels and possible breach of consent limits. In theory, such problems should be fairly easy to rectify by addition or removal of the incorrect nutrient(s) but it is clear that this has to be done with some degree of care as inappropriate action may worsen the imbalance or push the problem in the other direction. Normal wastewater measurements such as those for Biological Oxygen Demand, nitrogen and phosphorus may be used to determine the C:N:P ratio and we o er a number of carefully formulated nutrient solutions, both singly and in combination, to achieve the correct balance in the plant. Filamentous bulking is another signi• cant problem in wastewater treatment plants, a ecting most facilities at one time or another. As the name suggests • lamentous bacteria such as Beggiatoa, Microthrix, Nocardia and Sphaerotilus grow in long, thread-like strands and small numbers are useful in the active sludge process as they provide some degree of structure and allow the formation of larger, stronger • ocs, as well as helping to trap particulate matter. However overgrowth of these organisms causes bulking sludge with poor settling characteristics and excessive foaming. The causes of • lamentous bulking tend to be associated with particular bacterial species and include nutrient de• ciencies, low dissolved oxygen, low pH and excessive fat, oil and grease levels. It is important to identify the • lamentous organisms causing the problem in order to rectify the plant conditions that are encouraging them. We also o er a two- step treatment for • lamentous bulking problems – disrupting long • laments and surface foams and repopulating the system with • oc-forming bacteria. Biological Preparations' experts can advise on suitable methods of treatment to rectify nutrient imbalances, • lamentous bulking and other problems.