The cost of handling and disposal of sewage sludge is a major expense in sewage treatment. Often half of the treatment plant expense is in the purchase and maintenance of sludge handling equipment. The sludge problem becomes particularly acute with activated sludge processes because of the large volumes of waste activated sludge produced and the nature of the activated sludge itself. The object of this investigation was to conduct laboratory scale investigations of the effects of aerobic digestion on activated sludge dewatering and to attempt to determine the chemical and biological mechanisms affecting sludge filterability. The results of this investigation showed that aerobic digestion can have a considerable effect on sludge filterability. The filterability of all sludges was improved with moderate aeration at 20° C. The degree of improvement depends on the nature of the fresh sludge, the rate of aeration during digestion, the temperature during digestion, and the time of digestion with the optimum time of digestion between four to six days. The mechanism of filtration improvement during aerobic digestion appears to be biological in nature. Biologically produced extracellular polymeric substances are secreted by or exposed on the surface of bacteria during the endogenous phase of metabolism. These polymers cause coagulation and bridging between sludge particles, thus affecting the filtering properties. This phenomenon occurs only when oxygen is present in the system. However, the organisms responsible can survive up to four days without the artificial addition of oxygen. A study of various operating parameters in aerobic digestion leads to some further conclusions regarding sludge filtration. Factors which have a detrimental effect on filtration are: lack of dissolved oxygen, excessive mixing, low temperature during digestion, and chlorination of sludge before filtering. Factors which do not appear to have a significant effect on filtration are: differences in dissolved oxygen concentrations above two mg per liter, and the maintenance of a neutral pH in the digester. / Ph. D.

The purpose of this investigation was to determine what effect agitation had upon the biochemical oxygen demand of sewage. In order to determine the effect of agitation, the composition of the sewage, the seed source, the temperature and the dilutions were held constant. / Master of Science

The purposes of this study were to develop a reliable bench-scale testing procedure to adequately predict polymer conditioning requirements for full-scale belt filter presses, and to determine the additional polymer demand exerted by applied pressure during the expression stage of a dewatering process. Bench-scale experiments performed with anaerobically digested, alum, and secondary sludges used a high-speed mixer to gauge mixing intensity effects, and a wedge zone tester to gauge applied pressure effects on conditioning requirements. Full-scale experiments varied Sludge throughput, belt speed, and polymer dose to evaluate polymer performance. The polymer requirements to optimize performance of a full-scale belt filter press can be predicted with a bench-scale mixing device, where the shear (Gt) of the mixer matches that of the full-scale press. An estimate of the Gt value of the full-scale belt filter presses used in this study was 10,000. Alternatively, a bench-scale wedge zone tester, operated in an applied pressure range between 5 psi and 20 psi, can predict polymer doses for optimum belt filter press performance. The range of applied pressures used to simulate the expression phase of a dewatering process did not exert a Significant additional polymer demand for optimum conditioning. The shear (Gt) associated with mixing sludge and polymer during conditioning can exert a greater polymer demand than the expression phase of the wedge zone tester. / Master of Science

This research effort involved the application of indirect- and direct-contact, freeze-thaw conditioning techniques for improving the dewatering characteristics of both wastewater and water treatment sludges. Sludges tested included waste activated sludge, primary sewage sludge, waste activated/primary sewage sludge mixtures and alum sludge. The direct-freeze methods examined were the use of a secondary refrigerant (butane) evaporated in the sludge and the use of gas hydrate or clathrate formation by addition of Freon 12 under appropriate temperature and pressure conditions. Sludges were also frozen solid using indirect freezing methods, thawed and tested for comparative purposes. Particle size distribution and floc density measurements were used to determine changes in particle characteristics; specific resistance values and dewatered dry solids concentration were used to assess dewatering characteristics. Results of direct- and indirect-contact, freeze-thaw conditioning were compared to the effects of polymer conditioning. The results indicated that direct-freeze methods do not appear technically or economically competitive with currently accepted conditioning methods. The superior results obtained with the indirect-contact, freeze-thaw process when compared to the direct-contact processes suggested that the extent and rate of freezing may greatly influence the particle characteristics of the conditioned sludge, and thus its dewatering characteristics. / Ph. D.

Colloidal gas aphrons (CGAs) are typically a 55 to 70% dispersion of 50 +/- 40 micron-sized air bubbles in water. Generation of CGAs has proceeded to allow continuous production of up to 80 liters per minute. Previous laboratory testing has demonstrated the effectiveness of CGA flotation for removing fine particulates, such as coal fines, food wastes, phosphate slimes, algae, as well as oils from contaminated solutions. This study involved comparing CGA flotation versus dissolved air flotation (DAF) in a wastewater treatment sludge media. Initially, laboratory tests were conducted to see if field testing was warranted, and to screen possible surfactant chemicals to be used in any such field testing. Three surfactants were tested individually; sodium dodecylbenzene sulfonate (NaDBS), alkyl dimethyl benzyl ammonium chloride (BTC-824), and cetyl pyridinium chloride (CPC). From the laboratory results and observations, it appeared that the CGA flotation tests using both NaDBS and CPC were more effective than DAF. Tests using BTC-824 were inconsistent due to bubble instability. Overall, the laboratory results and observations seemed encouraging, and field testing was initiated. Next, four field tests were conducted at Pepper's Ferry Regional Wastewater Treatment Authority (PFRWTA) in which CGA flotation was used to try and enhance the performance of a DAF system. Tests were conducted by adding CGAs directly into the sludge influent line of PFRWTA's DAF system. Although CPC gave the best laboratory results, NaDBS was used in the field testing due to its availability and cost. Results from all four field tests showed that a more concentrated effluent sludge was obtained when CGA flotation was used to enhance DAF. The field test results for the raffinates were inconclusive. Overall, the results from the field testing seem promising. From these tests, CGA flotation appears to be an improvement over DAF in producing more concentrated effluent sludges when tested in a wastewater treatment sludge media. CGA flotation could enhance and/or possibly replace DAF in certain industrial applications. / Master of Science

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

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

The purpose of this study was to determine how chemical conditioning agents and mechanical dewatering devices affect sludge dewatering with respect to shear. Bench scale experiments were performed to determine the effect of shear and mole charge on polymer dose requirements using anaerobically digested sludge. Lime, ferric chloride, and polymer were used to condition anaerobically digested sludge to evaluate the influence of these conditioning agents, separately and in combination, on shear resistance. Dewatering studies were performed using a plate and frame press, a centrifuge, and a screw press to determine the amount of shear within each device and to develop a means of estimating polymer dose for each device. It was determined that increased molecular charge of polymer decreased chemical dose requirements and improved shear resistance. Both lime and ferric chloride improved sludge dewatering rates but only ferric chloride conditioned against shear. Ferric chloride addition prior to polymer conditioning improved sludge shear resistance, improved the dewatering rate (CST), and decreased the required polymer dose. The dewatering study using the plate and frame press verified that polymer dose could be estimated using CST values and a Gt value of approximately 30,000. Also, ferric chloride in combination with polymer improved filtrate quality, increased the cake solids concentration, and increased the filtrate volume throughput of sludge conditioned with lower polymer doses than if polymer alone was used. The dewatering study using a high speed centrifuge found that polymer dose could be estimated using CST values at a Gt between 10,000 and 20,000 or by use of the wedge zone simulator. The dewatering study of the screw press found that CST values and the wedge zone simulator under predicted polymer dose. This was thought to be the result of shear in the feed system prior to dewatering. / Master of Science

The purpose of this study was to investigate treatment alternatives for a leachate from a municipal landfill in Roanoke County, Virginia. A continuous flow, laboratory scale, single sludge waste treatment system utilizing the Modified Ludzack Ettinger (MLE) nitrification/denitrification process with the addition of phosphorus and methanol was operated to determine its effectiveness in removing total nitrogen, organic compounds and metals from the leachate. The system was compared with the effectiveness of a totally aerobic activated sludge system operated in various configurations and at different mean cell residence times (MCRT’s) with and without the addition of methanol. The ability of activated carbon to remove organics from the leachate was briefly examined. The early results from this study indicated that the MLE process could successfully treat the leachate by removing up to 84% of the total nitrogen present while operating at high MCRT’s (eight days or greater). The MLE process removed as much as 56% of the total nitrogen at the lowest MCRT operated (1.5 days), By comparison, a maximum removal of only 30% was achieved for the completely aerobic activated sludge system operating under the same conditions. The MLE process and the completely aerobic process were not effective in removing the organics from the leachate as evidenced by a leachate COD removal of only 2% to 5%. Limited studies with activated carbon proved successful in substantially reducing the COD from the effluent of the biological treatment systems. The MLE process consistently reduced the iron concentration in the leachate from the average level of 18.6 mg/l to levels below 1.0 mg/l. Towards the end of this 584-day study, there were indications that toxic agents were intermittently entering the leachate from the landfill as evidenced by two episodes of severe nitrification inhibition during operating periods when nitrification should have been essentially complete. This raises doubts concerning the ability of biological nitrification/denitrification to successfully treat the Dixie Caverns landfill leachate on a long-term basis without special treatment for the removal of the unknown toxic components. / Master of Science