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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

We 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 suitable conditions in terms of temperature, pH and aeration will optimise activity. However further modification of conditions may be required, for example to rectify nutrient imbalances or to manage the growth of filamentous organisms.

Nutrient balance is an important issue, as microbes require a particular nutrient ratio in order to carry out their activities at optimum efficiency. 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.

Often 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 deficient in certain industrial effluents. If the C:N:P ratio is not correct, microbial growth can be significantly limited and efficiency 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 offer a number of carefully formulated nutrient solutions, both singly and in combination, to achieve the correct balance in the plant.

Filamentous bulking is another significant problem in wastewater treatment plants, affecting most facilities at one time or another. As the name suggests filamentous 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 flocs, 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 filamentous bulking tend to be associated with particular bacterial species and include nutrient deficiencies, low dissolved oxygen, low pH and excessive fat, oil and grease levels. It is important to identify the filamentous organisms causing the problem in order to rectify the plant conditions that are encouraging them. We also offer a two-step treatment for filamentous bulking problems – disrupting long filaments and surface foams and repopulating the system with floc-forming bacteria.

Biological Preparations’ experts can advise on suitable methods of treatment to rectify nutrient imbalances, filamentous bulking and other problems.

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