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In recent years publicly owned treatment works (POTWs) have increasingly turned to thermal drying to treat municipal biosolids. Thermal drying significantly reduces the mass and volume of the biosolids which must be handled and typically produces a Class A product suitable for beneficial reuse. However, thermal drying systems can be sensitive to changes in operating conditions. If the percent solids of either the feed to the dryer or the material inside the dryer move outside of acceptable ranges, dryer process malfunction can result, causing significant operational and maintenance problems. Therefore, establishing acceptable ranges of the percent solids of the material and monitoring those ranges during operation is critical to establishing smooth drying system operation.This paper examines the commissioning and optimization of the thermal drying system installed as part of the Alternative Solids Project (ASP) at the Morris Forman Wastewater Treatment Plant (WWTP), which is owned and operated by the Louisville and Jefferson County Metropolitan Sewer District. During commissioning of one of the largest drying systems in the country, operational difficulties were encountered for several reasons. Some of the difficulties were the normal process of learning acceptable operating conditions through trial and error, while others were related to temporary upstream facilities, which resulted in inconsistent feed characteristics to the dryers and undigested sludge to process. To address process malfunctions, a set of optimization procedures were established to monitor solids concentrations of the feed to the dryer and at several internal dryer locations. Procedures were also established to correlate the solids concentrations data with process malfunctions to establish acceptable operating ranges for each of the locations monitored. The optimization plan was implemented and proved to be a successful tool in predicting when process malfunctions would occur. Use of the plan has significantly reduced the number of process malfunctions, which in turn has increased the availability of the dryers and reduced maintenance and landfill costs. BACKGROUND

Excessive foaming in anaerobic digesters has been a problem for many years. All anaerobic digestion will foam to some extent, but excessive foam can be problematic. Excessive foaming is defined as foam that interferes with flow through the gas piping system and/or is not contained within the digester. Causes for foaming include presence of excessive filamentous bacteria, excessive oils and grease, and the feed sludge composition -primary sludge (PS) versus waste activated sludge (WAS), but the chief cause of excessive foaming is inconsistent feed to the digesters.Monitoring and consistent feeding are vital to successful digester operation and to minimizing excessive foaming events. Three case studies will be presented demonstrating an effective monitoring program to control volatile solids loading to the digester were used to eliminate excessive foaming events. Following the case studies a general discussion of recommended operational strategy is presented, and conclusions.

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Organic overloading from an industrial source and a blower malfunction combined to cause a BNR nitrogen removal plant to self-destruct. This is a story about the Glendale WWTP at Lakeland Florida, a 13.7 mgd facility that suffered a major process upset. Unlike other activated sludge plants experiencing organic overloading, this plant resisted conventional recovery efforts. Chlorinating RAS and re-establishing a good dissolved oxygen profile in the oxic zone did not result in system recovery. Quite to the contrary, filaments continued to flourish.After three weeks of frustration and only transitory successes in improving mixed liquor settleability (SVI), nitrification was lost. Staff had to ask "What are we doing wrong?" The facility should have been well on the road to recovery but it wasn't. A sample of MLSS was sent out for analysis and the report indicated O21N predominated, with Thiothrix I also present. These two organisms, O21N and Thiothrix I, both thrive under septic conditions. Many times, the definition for septic conditions means only a lack of dissolved oxygen. Restoring the DO concentration was not working. After more investigation, the definition of septicity was found to also include high concentrations of acetic acid or volatile fatty acids (VFA). It was found that the VFA concentration in the influent to the activated sludge process was high.A two-pronged remedy was developed. A nitrate solution was fed to the anoxic zones in the activated sludge basins to use the nitrate oxygen source to consume VFA under anoxic conditions. Reducing the VFA concentration in the anoxic zone could sufficiently lower the aerated zone influent VFA concentrations to allow the conventional floc forming bacteria to out-compete the filaments for food. Chlorination of RAS was continued to kill the accumulated filaments. KEYWORDSO21N, Thiothrix I, volatile fatty acids, anoxic zones, nitrate reduction 8428 WEFTEC®.07