Paul H. King’s research while affiliated with Virginia Tech and other places

The activated sludge process can remove significant amounts of phosphorus from sewage, but the removal efficiency is usually significantly reduced by the release of phosphate back to solution during subsequent treatment steps. This research presents a study of soluble phosphate release from activated sludge with emphasis on defining the factors that affect such release and the actual release mechanisms. Laboratory units were used for experimental purposes. The experiments were designed to study the relationship between soluble phosphate release and various environmental factors such as redox potential (ORP), dissolved oxygen (DO), pH, solids concentration, solids destruction, and sulfate salt addition. The effect of substrate utilization on phosphate uptake and the relationship between uptake characteristics and subsequent phosphate release were also studied. The results show that some phosphate storage occurs during aerobic substrate utilization. Following substrate utilization, activated sludge phosphate release is directly related to the amount of biological stress the organisms are subjected to, and the mechanism of release is primarily cell lysis. The phosphate released per unit sludge under anoxic conditions is relatively constant. Under normal environmental conditions, neither ORP or pH change have a significant affect on phosphate release.

The paper reports on a study to evaluate the thickening characteristics of four types of coagulant-aided primary sludges resulting from the application of alum, alum plus polymer, ferric chloride and ferric chloride plus polymer raw domestic wastewater. Solids flux analysis was the major tool utilize evaluation of the results of the thickening research. Laboratory studies were conducted to determine the relationship of selected coagulants/precipitants to the settling velocity of the sludge and to its limiting solids flux under varying conditions. In addition, the effects of initial sludge height and solids concentration, column diameter, slow stirring, and sludge aging and shearing were defined.

A review of the literature is presented and discussed on the chemical precipitation methods utilizing lime and alum metallic salts that remove high levels of phosphorus from wastewater. Although either salt can be used, lime sludges were found to dewater more satisfactorily while not needing polymer conditioning. Alum sludges, when properly conditioned, allowed faster sand-bed turnover and an increasing rate of gravity drainage. The most feasible approach to phosphorus removal depends upon specific conditions of each locality and various other factors as discussed.

The past decade has seen the intensification of enforcement activities by water pollution control regulatory agencies and with it, the subsequent realization by water utilities that sludge disposal costs may be a substantial portion of water production budgets. No longer can sludge management at water treatment plants be considered as an afterthought in process selection and design. In many cases the nature and amount of sludges generated in water purification will be controlled by chemical considerations relating to both the raw water quality and the treatment process applied to the particular situation. Major sources of wastes from water treatment include chemical coagulation and sedimentation, granular bed filtration, lime-soda softening, and ion exchange softening. Of somewhat lesser current importance are presedimentation, iron and manganese removal, activated carbon treatment, diatomaceous earth filtration, and fluoride removal. This paper reviews the important chemical considerations in the generation, treatment, and disposal of wastes from the most frequently employed water treatment processes.

Laboratory studies were conducted to evaluate the relative effectiveness of chlorination and acidity in the conditioning of selected primary, anearobically digested, and aerobically digested sludges. Principal parameters of interest were filterability of sludge after conditioning as determined by specific resistance, release of organic material to the filtrate during conditioning as indicated by chemical oxygen demand, and release of typical metals, including zinc, copper, and chromium, during conditioning. The results indicated that many of the beneficial effects of the chlorine oxidation process are the result of acid treatment alone and are not dependent on the addition of large dosages of chlorine. The work also showed that application of chlorine may increase possibly deleterious effects in the conditioning process.

This article discusses various technical and economic aspects of alum recovery from different sludges for coagulant reuse.

A laboratory study was conducted to compare the response of an activated sludge culture proliferating in an environment where the DO concentration was maintained between 8-9 mg l–1 to that of a culture in an environment where the DO concentration was 2 mg l–1 when both systems were subjected to identical loading fluctuations. It was observed that in the high DO system, filamentous microorganisms became the predominate form when the suspended solids concentration dropped below a value near 4000 mg l–1. However, no filamentous growth appeared in the alternate system until the suspended solids level dropped below 500 mg l–1. A model is developed which proposes to explain this observation.

The effects of temperature upon the kinetics of waste activated sludge aerobic digestion in batch reactors were studied. Reactors were maintained at temperatures of 5°C, 10°C, 20°C, 30°C, 35°C, and 45°C ± 1°C, and the changes in suspended solids concentration, oxygen uptake rate, pH, specific resistance and flow particle size of the mixed liquor, as well as pH, BOD, and TOC of the supernatant, with digestion time, were measured. The specific decay rate was not affected in an Arrhenius fashion above 20°C, and the greatest solids reduction occurred in the 20°C reactor over a 15 day digestion period. A significant portion of the suspended solids destroyed at 45°C are solubilized but the soluble organics are not metabolized, therefore, the true stabilization at 45°C is somewhat less than the apparent stabilization calculated from suspended solids reduction. There appears to be no practical advantage to aerobic digestion temperatures in excess of 20°C.

The results of a study conducted by the ASCE EED Committee on Water Purification aimed at determining the prevailing concept of 'high rate' water treatment are presented. A survey of state regulatory agencies gained information in terms of attitudes and policies. In addition, an analysis of operating data from several high rate water treatment plants in Virginia was conducted. Specific data are given for acceptable flash mixing, flocculation and sedimentation retention times, and for hydraulic loading rates of sand and multimedia filtration systems. The possible requirement of polymer feed capability and special process control equipment in high rate filtration installations is considered. A total of over 200 plants operating at filtration rates in excess of 3 gpm/sq ft were identified. The economic advantages inherent in these processes make it incumbent on the design engineer to thoroughly evaluate their applicability in any situation.

The effects of temperature upon the kinetics of waste activated sludge aerobic digestion in batch reactors were studied. Reactors were maintained at temperatures of 5°C, 10°C, 20°C, 30°C, 35°C, and 45°C—1°C, and the changes in suspended solids concentration, oxygen uptake rate, pH, specific resistance and floc particle size of the mixed liquor, as well as pH, BOD, and TOC of the supernatant, with digestion time, were measured. The specific decay rate was not affected in an Arrhenius fashion above 20°C, and the greatest solids reduction occurred in the 20°C reactor over a 15-day digestion period. A significant portion of the suspended solids destroyed at 45°C are solubilized but the soluble organics are not metabolized, therefore, the true stabilization at 45°C is somewhat less than the apparent stabilization calculated from suspended solids reduction. There appears to be no practical advantage to aerobic digestion temperatures in excess of 20°C.