Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Includes bibliographical references. / Ph.D.

Conditioning studies were conducted on several water and wastewater sludges using polymers to determine the effect of high-intensity mixing on floc formation and breakup. Mechanisms acting in particle coagulation were also investigated. A rapid mixing apparatus was used in conditioning the sludge to simulate the high velocity gradients encountered in most dewatering equipment. Anionic and cationic polymers of varying molecular weights and an inorganic coagulant were chosen as the conditioning agents. Dewatering rates were measured by the capillary suction time (CST) apparatus. The effect of rapid mixing on the polymer efficiency was evaluated by premixing the polymer, using the same mixing apparatus, prior to applying it to condition the sludge. Data analyses revealed the great impact the primary floc breakup has on the sludge dewatering rate, although this was shown to be dependent on the nature of the sludge particles. Some minor changes were imparted to the polymer chains by intense mixing but there was no evidence that particle polymer bonds were fractured. The mechanisms of coagulation were observed to be related to sludge type. Overall, successful conditioning of sludges by polymers requires a proper determination of the sludge characteristics, a correct choice of polymer type and dose, and a knowledge of the mixing intensities. / Master of Science

The effects of coagulation pH and influent turbidity on aluminum and ferric hydroxide sludge macro-and micro-properties were investigated. To reduce the number of variables, sludges were produced under specific operating conditions in a 400 L/day continuous-flow pilot-plant. The effluent turbidity was monitored to evaluate process modifications. Sludge thickening and dewatering characteristics improved with reductions in the coagulation pH, increases in the influent turbidity levels, and/or reductions in the coagulant dose/influent turbidity ratio. Sludge floc/ aggregate density was the dominant sludge micro-property; sludges with superior thickening and dewatering characteristics were composed of higher density flocs/aggregates. A trade-off appeared to exist between improved sludge characteristics and effluent quality; however, verification will require additional research. / M.S.

M. S.

Separation of liquid from solids is a necessary step in the ultimate disposal of wastewater sludges. Most commonly, sludges are dewatered by pressure-filtration methods. Mathematical models of the physics of the sludge dewatering process would provide the ability to predict dewatering performance and optimize the design and operation of dewatering facilities.

The differences in pollutant export from identical land areas treated with fertilizer and/or composted domestic wastewater sludge (compost) were evaluated. Three plots were constructed with a Glenelg silty clay soil and seeded with Falcon fescue (Festuca 'Falcon'): Plot 1 received conventional fertilizer; Plot 2 received a combination of compost and reduced conventional fertilizer; and Plot 3 received only compost. Runoff was collected and analyzed for soluble orthophosphate as P, total soluble phosphorus as P, total phosphorus as P, soluble ammonia as N, soluble Kjeldahl nitrogen as N, total Kjeldahl nitrogen as N, nitrite plus nitrate as N, total suspended solids, chemical oxygen demand, cadmium, copper, lead, nickel, zinc, chromium, and iron. Compost was found to improve moisture retention in the soil and crop, sustain plant growth during excessive dry periods, improve the quality of the crop, reduce runoff, and reduce soil erosion. The export of all pollutants was reduced by the use of compost. The use of fertilizer in combination with the compost did not provide any observable benefit. Instead, the fertilizer provided excessive soluble orthophosphate, total soluble phosphorus, and oxidized nitrogen which were subsequently exported from the test plot. The increased export of soluble Kjeldahl nitrogen may have been caused by excess insoluble N from the fertilizer application, which may have reacted with the organic matter, forming soluble organic nitrogen. The use of compost as a soil amendment significantly reduced the pollutant export which, in turn, reduced the potential impact on receiving waters. / M.S.

Experiments were performed on samples of alum and activated sludges to determine if these sludges, conditioned with polymers under high-stress, would achieve favorable dewatering rates. Tests were conducted using a variable high speed mixer with root mean square velocity gradient (G) values ranging from 560 - 2000 sec⁻¹ with both anionic and cationic high molecular weight polymers. Capillary suction time (CST) was used to measure relative changes in dewatering rates. Results indicated that readily dewatered sludges can be obtained when subjected to high-stress mixing conditions. The most significant parameters governing high-stress conditioning were determined to be polymer dose and total mixing energy input (Gt). It was discovered that as Gt increases, polymer dose requirements increase as well, so as to maintain an optimum dewatering rate. Also, the activated sludges tested in the study appear to be resistant to the effects of polymer overdosing. / M.S.

Experiments were performed on alum, anaerobically digested and aerobically digested sludges to determine the optimum polymer conditioning for a belt filter press The optimum polymer dosages for all three zones of a belt filter press were compared with each other to determine the best overall conditioning. The requirements of all three zones of a belt filter press were the same. However, the gravity rate of drainage seems to under predict the dosages for optimum belt filter press performance. In addition the total mixing energy, G (the shear) and t (the mixing time), that represents the laboratory belt filter press was found to be approximately 45,000. Using a mixing energy input of 45,000 and a standard Buchner funnel apparatus the correct polymer dose for the belt filter press can be predicted. / Master of Science

Floc density measurements may play a significant role in analyzing sludge dewatering characteristics. A laboratory technique was developed to measure this property by means of isopycnic centrifugation. Four laboratory sludges were subjected to a series of dewatering tests: gravity thickening, centrifugation, vacuum filtration, and high-pressure dewatering. Each sludge was analyzed for changing macro- and micro-properties during increasing stages of dewatering. It was concluded that sludge thickening rates are influenced by aggregate volume fractions, sludge density, suspension porosity, and the total surface area occupied by sludge aggregates. The extent of mechanical dewatering is impacted by similar parameters; namely, floc volume fractions, sludge density, cake porosity, and the total surface area occupied by sludge floc. By interpreting the laboratory data, a model was formulated to describe changes in water distribution during the dewatering of sludges. This model includes a speculative view of the qualification and quantification of water-types. / Master of Science

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management