Waste sludge is frequently treated by anaerobic digestion to kill pathogens, generate methane gas and reduce odors so the sludge can be safely land applied. In an attempt to reduce sludge volumes and improve sludge dewatering properties, the use of thermal hydrolysis (TH), a sludge pretreatment method, has been adopted by numerous wastewater treatment plants, among them being the District of Columbia Water and Sewage Authority (DC WASA). The use of anaerobic digestion in collaboration with thermal hydrolysis has been shown to increase VS removal, COD removal and biogas production. The sludge generated also dewaters to a higher cake solids than from conventional anaerobic digestion. Unfortunately, DC WASA has found that the use of thermal hydrolysis had brought about two major issues. These are: (a) does thermal hydrolysis increase destruction of fats, oils and greases compared to conventional digestion? and (b) is the mixing method used at Virginia Tech (recirculating gas mixing) capable of stripping ammonia from the digester? Therefore the main purpose of this study is to evaluate these issues which occur with the use of the thermal hydrolysis process. Experiments were conducted in two phases. The first phase was to assess the performance of anaerobic digesters via their biogas production with and without long chain fatty acid addition and with or without thermal hydrolysis. This research was further carried out in two stages. First a mixture of unsaturated long chain fatty acids (hydrolyzed and unhydrolyzed) was used. The fatty acid mixture included oleic, linoleic and linolenic acids, which contain one, two and three double bonds, respectively. In the second stage, the effect of a single unsaturated fatty acid (hydrolyzed and unhydrolyzed) was analyzed. If extra gas is generated, grease addition to the digesters will be implemented. If thermal hydrolysis produces more gas, the greases will be added through the thermal hydrolysis unit rather than being added directly to the digester. The results showed that addition of long chain fatty acids greatly increased gas production and the long chain fatty acids that were thermally hydrolyzed generated more gas than the untreated long chain fatty acids, although the gain was not large. The second phase of the study was carried out by alternating the type of recirculating gas mixing (partial and continuous) in the anaerobic bioreactor. To achieve this goal, short-term anaerobic bioreactor studies were conducted by varying the frequency of the gas. The result showed that continuous gas recirculation at the bottom of the digester was responsible for stripping ammonia from the system. It appeared that up to 500 mg/L of ammonia was being stripped from the digester operating at 20 day solids retention time. This suggests that ammonia can be stripped if a reduction of ammonia in the digester was desired. / Master of Science

An investigation was carried out to study whether long-chain fatty acids (LCFAs) have an effect on digestion of waste sludge under anaerobic conditions. Four different kinds of LCFAs were used in this study. The 18 carbon series with 0, 1, 2 and 3 double bonds were studied to evaluate the degree of saturation on fatty acid degradation. Due to their molecular structure, unsaturated LCFAs are more soluble than saturated LCFAs. Oleic, linoleic, linolenic acid with an ascending number of double bonds were tested as representatives for three different degrees of saturation. In addition, stearic acid, a saturated fatty acid was also tested. LCFAs were added to sewage sludge at concentrations ranging from 5% to 20% on a weight basis and the pH, solids reduction and COD reduction were determined. The results suggested that in addition to degrading in the digesters, all unsaturated acids contributed additional solids removal, compared to the control group. In contrast, stearic acid did not affect the solids removal. The COD reduction was similar to solids reduction in that additional COD was destroyed when unsaturated LCFAs were added to the sludge. The mechanism for additional solids reduction is not known. / Master of Science

Anaerobic digestion of wastewater sludge has widely been in application for stabilization of sludge. With the increase in hauling cost and many environmental and health concerns regarding land application of biosolids, digestion processes generating minimized sludge with better effluent characteristics is becoming important for many public and wastewater utilities. This study was designed to investigate the performance of anaerobic-aerobic-anaerobic digestion of sludge and compare it to anaerobic-aerobic digestion and single stage mesophilic digestion of sludge. Experiments were carried out in three stages: Single-stage mesophilic anaerobic digestion (MAD) 20d SRT; Sequential Anaerobic/Aerobic digestion (Ana/Aer); and Anaerobic/Aerobic/Anaerobic digestion (An/Aer/An). The Anaerobic/Aerobic/Anaerobic digestion of sludge was studied with two options to determine the best option in terms of effluent characteristics. The two sludge withdrawal options were to withdraw effluent from the anaerobic digester (An/Aer/An – A) or withdraw effluent from the aerobic digester (An/Aer/An – B). Different operational parameters, such as COD removal, VS destruction, biogas production, Nitrogen removal, odor removal and dewatering properties of the resulting biosolids were studied and the results were compared among different processes. From the study, it was found that An/Aer/An – B (wastage from aerobic reactor) provided better effluent characteristics than An/Aer/An – A (wastage from anaerobic reactor), Ana/Aer or conventional MAD. The study also shows that the Anaerobic/Aerobic/Anaerobic (An/Aer/An, with wastage from the aerobic or anaerobic digester) digestion of the sludge can improve the biosolids quality by improving the dewatering capabilities, with lower optimum polymer dose, reduced CST and increased cake solid concentration, and reduce the odor generation from the biosolids. Both An/Aer/Ana – A and An/Aer/An – B gave 70% VS removal, compared to 50% with single MAD and 62% with only Ana/Aer. COD removal of both An/Aer/An – A and An/Aer/An – B was 70%, while it was 50% and 66% for single MAD and Ana/Aer respectively. In the aerobic reactors of Ana/Aer and An/Aer/An - B, nitrification and denitrification with removal of nitrogen was observed. The An/Aer/An – B system had more ammonia and TKN removal (70%) than Ana/Aer (64%). The effluent from each stage was analyzed for dewatering ability, cake solid concentration and odor production potential. Compared with a single Ana/Aer system, the extra anaerobic step in An/Aer/An – A and – B reduced polysaccharides in the effluent. The Ana/Aer system released less protein than the conventional MAD system and the addition of the second anaerobic step - especially with system An/Aer/An – B (discharge from aerobic reactor) - greatly reduced protein, resulting in improved dewaterability and less polymer demand. An/Aer/An (both of the options: A and B) had lower CST than single MAD (both 15d and 20d SRT) and Ana/Aer. Compared to Ana/Aer, a reduction of 52% for An/Aer/An – A and 20% for An/Aer/An – B in polymer dose requirement was observed, indicating improved dewatering characteristics. The An/Aer/An – B has higher biosolid cake concentration than MAD or Ana/Aer. The results showed that An/Aer/An (both options: A and B) biosolid had lower odor generation potential than single MAD (15d and 20d SRT) or Ana/Aer. Of all the stages,the An/Aer/An – A and – B system, generated odor which peaked at shorter time and lasted for shorter duration of time. / Master of Science

The increased demand for advanced techniques in anaerobic digestion over the last few years has led to the employment of various pre-treatment methods prior to anaerobic digestion to increase gas production. These pre-treatment methods alter the physical and chemical properties of sludge in order to make it more readily degradable by anaerobic digestion. The thermal hydrolysis process has been used in several treatment plants around the world, but none currently operate in the US. Thermal hydrolysis causes cell walls to rupture under the effect of high temperature and high pressure and results in highly solubilized product which is readily biodegradable. The performance of the process was evaluated for a treatment plant located in Dallas, TX. The performance assessment was based on various characteristics including pH, solids removal, COD removal and gas production. The study was conducted in two phases to investigate the effect of change in mesophilic temperature (37°C and 42°C) and the effect of solids retention time (SRT) (15 days and 20 days). Thermally hydrolyzed combined (1:1) primary and waste activated sludge was fed to a Thermal Hydrolysis (TH) anaerobic digester and its performance was compared to a conventional mesophilic anaerobic digester receiving non pre-treated sludge. The thermal hydrolysis pre-treatment was found to be more effective as compared to the conventional anaerobic digester. The efficiency of the process varied slightly with increase in temperature but the change in SRT was seen to have a greater impact on the digester's performance. The pre-treatment technique was observed to deliver the best results at a 20 day SRT. / Master of Science

Sludge digestion has gained importance in recent year because of increasing interest in energy recovery and public concern over the safety of land applied biosolids. Many new alternatives are being researched for reducing excess sludge production and for more energy production. With an increase in solids destruction, the nutrients that are contained in sludge especially nitrogen, are released to solution and can be recycled as part of filtrate or centrate stream. Nitrogen has gained importance because it has adverse effects on ecosystem's as well as human health. NH₄⁺, NO₂⁻, NO₃⁻-, and organic nitrogen are the different forms of nitrogen found in wastewater. While ammonia is toxic to aquatic life, any form of nitrogen can be utilized by cyanobacteria and result in eutrophication. NO₂/NO₃, if consumed by infants through water, can affect the oxygen uptake capability. Hence, removal of nitrogen from wastewater stream before discharging is important. The main purpose of this study was to evaluate the performance of the Cambi process, a thermophylic hydrolysis process used as a pre-treatment step prior to anaerobic digestion. Thermal hydrolysis, as a pre-treatment to anaerobic digestion increases the biological degradation of organic volatile solids and biogas production. The thermal hydrolysis process destroys pathogens and hydrolysis makes the sludge readily available for digestion, while at the same time facilitating a higher degree of separation of solid and liquid phases after digestion. Experiments were conducted in three phases for anaerobic digestion using the Cambi process as pre-treatment. The phases of study includes comparison of two temperatures for thermal hydrolysis (Cambi 150°C and Cambi 170°C), comparison of two solid retention times in anaerobic digestion (15 Day and 20 Day) and comparison of two mesophilic temperatures in anaerobic digestion (37°C and 42°C). Different experimental analyses were conducted for each phase, such as pH, bio-gas production, COD removal, VS destruction, nitrogen removal, odor and dewatering characteristics and the results are compared among all the phases. The second part of the study deals with aerobic digestion of anaerobically digested sludge for effective nitrogen removal and additional VS destruction, COD removal. An aerobic digester is operated downstream to anaerobic digester and is operated with aerobic/anoxic phase for nitrification and de-nitrification. The aerobic/anoxic phases are operated in time cycles which included 40minutes/20minutes, 20minutes/20minutes, full aeration, 10minutes/30minutes, and 12minutes/12minutes. Different time cycles are experimented and aerobic digester is optimized for effective nitrogen removal. 12minutes aerobic and 12minutes anoxic phase gave better nitrogen removal compared to all the cycles. Over all the aerobic digester gave about 92% ammonia removal, 70% VS destruction and 70% COD removal. The oxygen uptake rates (OUR's) in the aerobic digester are measured corresponding to maximum nitrogen removal. The OUR's are found to be close to 60 mg/L during maximum nitrogen removal. The effluent from both anaerobic digester and aerobic digester was collected and analyzed for dewatering capability, cake solids concentration and odor potential. / Master of Science

This thesis is an investigation on water reuse in the fresh-cut fruits and vegetable industry. Fresh water is used intensively in washing, cutting/peeling processes and disinfecting fruits and vegetables, as a result washwater with heavy solids is generated. Effective removal of solids is needed to allow for water reuse. Thus dissolved air flotation (DAF) and centrifuge with coagulation and flocculation process were explored for solid removal capabilities; some settling analysis was also conducted. Bench scale studies show DAF and centrifuge produce waters of similar quality (Turbidity). DAF is able to produce waters with higher UV transmittance and can work better with membrane filtration and UV disinfection. While centrifuge showed higher reduction in pathogen levels, it can be cost effective and compact in design. Membrane filtration feasibility showed that high quality waters (low turbidity) can be produced, but were unable to remove pathogens. Collimated beam results show UV disinfection can further be used to completely eliminate pathogens and allow for water reuse. This allows the processors to reduce their water foot-print, increase sustainability of their operations, and meet the increasing demand for fresh-cut fruits and vegetables.

Sediment control devices (SCDs) are critical to reducing the contamination of waterways from adjacent construction sites. Perimeter sediment controls retard the flow of surface runoff water originating on site and subsequently reduce solid, nutrient, and metal concentrations suspended in the flowing water. Silt fence is a commonly used SCD comprised of geotextile filter fabric, steel or wood support posts, and wire mesh reinforcement. The Georgia Department of Transportation (GDOT) uses an extensive amount of silt fence every year, and because of high degradation of geotextile in the field, the silt fence installations are rarely recycled. This research measures the performance of five SCDs (two types of silt fence, mulch berm, compost sock, and straw bales) at suspended solid, turbidity, nutrient, and metal reduction. A life cycle analysis (LCA) is performed to identify environmental impacts associated with material production, assembly, installation, use on site, and disposal. An impact analysis is performed according to for each SCD. Results of the impact analysis are compared to determine the SCD with lowest overall environmental impact. Results of the SCD performance study show that silt fence installations performed the best at reducing suspended solids and turbidity, mulch was best at reducing nutrients, and compost was the best at reducing metal concentrations. The life cycle impact analysis indicates that a mulch berm is the SCD with the lowest overall environmental impact. The impact analysis included global warming potential, acidification, eutrophication, and aquatic toxicity.