Cavalcanti P, van Haandel A, Lettinga G
Department of Civil Engineering, Federal University of Paraíba, Campina Grande Pb, Brazil.
Water Sci Technol. 2002;45(1):75-81.
When ponds are used for wastewater treatment, settleable solids will form a steadily growing bottom sludge layer, which reduces their effective volume. Eventually this sludge must be removed to ensure that the pond maintains the required retention time to keep performing properly. The settleable solids may either be present in the influent or they are formed during the treatment as a result of algal flocculation. An experimental investigation was carried out to evaluate bottom sludge accumulation in a polishing pond used for treatment of UASB effluent. The mass and composition of the bottom sludge formed in a polishing pond was evaluated after the pilot scale pond had been in operation for 1 year and about 60 m3 of digested wastewater had been treated per m3 of pond. The bottom sludge mass represented a solids accumulation of 70 g per m3 of digested wastewater. About half of these solids were the result of settling of influent solids in the first part of the pond, while the other half was attributable to settling of algae, formed in the pond. It is concluded that the bottom sludge growth in a polishing pond is so low, that desludging during the useful life span of the pond will most likely not be necessary. This leads to the important conclusion that excess sludge discharge from UASB reactors (a major factor in operational costs) may be omitted, if a polishing pond is used for post-treatment. The bottom sludge had a high volatile solids concentration (58%) and the macronutrient fractions were also high (3.9% N and 1.1% P of the TSS mass). The bottom sludge was stable and could be dried directly without problems. The hygienic quality of the bottom sludge was very poor: about half the influent helminth eggs during one year of operation were found in the bottom sludge and the faecal coliform concentration was very high.
当利用池塘进行废水处理时，可沉降固体将形成一个不断增厚的底部污泥层，这会减小池塘的有效容积。最终，必须清除这些污泥，以确保池塘保持所需的停留时间，从而持续正常运行。可沉降固体可能存在于进水当中，也可能是在处理过程中由于藻类絮凝而形成的。开展了一项实验研究，以评估用于处理UASB出水的抛光塘中底部污泥的积累情况。在中试规模的池塘运行1年且每立方米池塘处理了约60立方米消化废水之后，对抛光塘中形成的底部污泥的质量和成分进行了评估。底部污泥质量相当于每立方米消化废水积累了70克固体。这些固体中约一半是进水固体在池塘前部沉降的结果，另一半则归因于池塘中形成的藻类的沉降。得出的结论是，抛光塘中底部污泥的生长速度非常低，因此在池塘的使用寿命期间很可能无需清淤。这引出了一个重要结论：如果使用抛光塘进行后处理，则可以省去UASB反应器排出的剩余污泥（运营成本的一个主要因素）。底部污泥的挥发性固体浓度很高（58%），常量养分含量也很高（占总悬浮固体质量的3.9%氮和1.1%磷）。底部污泥性质稳定，可以直接干燥，没有问题。底部污泥的卫生质量很差：在一年的运行期间，约一半的进水蠕虫卵都在底部污泥中被发现，而且粪便大肠菌群浓度非常高。
