Yes / An Euler-Lagrange CFD model is applied to a full-scale, biogas-mixed anaerobic digester to improve mixing efficiency and improve overall performance. Two quantitative mixing criteria previously adopted in anaerobic digestion (viz., uniformity index and dead volume) are critically assessed for the first time. A novel qualitative method is introduced to clarify the output of the quantitative methods. The first-ever quantitative assessment of mixing quality in full-scale, biogas-mixed anaerobic digestion is then proposed, and a strategy to improve mixing, involving the combined use of concentric nozzle manifolds at the base of the digester, is evaluated. / University of Birmingham (UK) Postgraduate Teaching Assistantship award; University of Bradford (UK) Postdoctoral research assistant contract, who provided financial support

A series of lab-scaled digestion studies including conventional mesophilic anaerobic digestion(MAD), thermophilic anaerobic digestion (TAD) at a range of treatment temperatures, and mesophilic high solids digestion of thermally pretreated wastewater sludge (THD) were carried out. Enhanced digestion performance in terms of solids destruction and methane generation by THD relative to MAD was achieved, and was largely attributable to the solubilization and subsequent biodegradation of energy-rich substrates within blended primary and secondary sludge. TAD was observed to underperform MAD, especially at elevated temperatures as methanogenic inhibition resulted in the accumulation of headspace hydrogen, thus resulting in poor removal of volatile fatty acids. The thermodynamics of fatty acid metabolism was favorable at each digestion temperature, thus it was concluded that microbial inhibition was the controlling factor in poor thermophilic performance. Inhibition by free unionized ammonia (NH₃) was characterized for THD and MAD biomass. Acetic acid degradation was equally affected over a range of NH₃ concentrations; however, methane generation by THD was less sensitive to ammonia inhibition, thus suggesting that methanogenesis by THD was less dependent on the NH₃-sensitive process of aceticlastic methanogenesis. Total ammonia nitrogen (TAN) and bicarbonate alkalinity were stoichiometrically produced from proteinaceous material during thermal hydrolytic pretreatment and subsequent high solids anaerobic digestion. Combined effects of TAN and high pH resulted in NH₃-inhibition during THD. Kinetic evaluations suggested that a growth rate reduction of approximately 65% was associated with in-situ NH₃ concentrations of the THD reactor. NH₃-inhibition was apparently responsible for a shift in dominant methanogenic community of the aceticlastic Methanosarcina barkeri in MAD to the hydrogenotrophic Methanoculleus bourgensis in THD. A similar shift in methanogenic community was observed between low temperature thermophilic digestion at 47°C, where the dominant order was Methanosarcinales, to high temperature thermophilic digestion at 59°C where the dominant order was Methanobacteriales. These findings support a process-driven pathway shift from aceticlastic to non-aceticlastic methanogenesis between 180 and 290 mg/L NH₃-N. Such a threshold is supported by previous literature related to ammonia tolerance of pure cultures of methanogens and has significant implications for the kinetic design of advanced anaerobic digestion processes. / Ph. D.

Addition of iron to sewer lines for chemical phosphorus removal is widely practiced around the world. However, high dosage of iron may prove detrimental to the anaerobic digestion process and also lead to higher organic sulfur odors and deteriorating biosolids quality. The following research focuses on finding an alternative to the use of iron in wastewater systems by comparing the roles of iron and magnesium on mesophilic anaerobic digestion, the digested effluent characteristics and odors in biosolids. Three anaerobic digesters were operated, one serving as a control with no additives, and the other two having known doses of iron and magnesium added. Comparison of the effluent characteristics revealed an improvement in the overall performance of the magnesium amended digester (in terms of pH, solids and COD reduction, alkalinity and gas production) over the other two reactors, suggesting the benefits of magnesium addition. Both iron and magnesium were found to be effective in achieving high levels of phosphate removals and reducing nuisance odors in dewatered sludge cakes. / Master of Science

Anaerobic digestion has been the preferred method for reducing and stabilizing waste sludge from biological wastewater treatment for over a century; however, as sludge volumes and disposal costs increase, there has been a desire to develop various methods for reducing the volume of sludge to be treated, improving the performance of the digesters, and increasing the energy value of the sludge. To this end, there have been numerous pretreatment and side-stream systems studied and developed over the past several decades with the overall goal of reducing the volume of biosolids to be disposed of in landfills or by land application. These technologies can be broken into four large groups: mechanical, thermal, chemical and biological, although there is often overlap between groups. This research approached the evaluations of these technologies through several methods in the hopes of developing effective tools for predicting the performance of each technology. Batch digestion studies mimicking several of these treatment methods and extensive analytical work on samples from full-scale installations were conducted to determine the effectiveness of each technology. From these studies a simple batch digestion methodology was developed to analyze the effectiveness of the Cannibal solids reduction process on wastewater streams that have never been exposed to it. Batch digestion of sludges pretreated with ozone, mechanical shear and sonication provided insight into the effectiveness of each technology. Extensive analytical work on samples collected from full-scale installations of thermal hydrolysis, mechanical shear and the Cannibal process provided some insight into the workings of each process and potential leads as to how to further characterize and evaluate each process. / Master of Science

In order to study the performance and mechanisms of excess sludge reduction in the activated sludge that incorporates the Cannibal™ Process, laboratory activated sludge systems incorporating an anaerobic bioreactor into the sludge recycle stream were operated. In this study, the solids production in the Cannibal system was about 35-40% of the conventional system under steady state conditions. The reduction in waste sludge was optimized when the interchange rate, (the ratio of sludge fed from the activated sludge system to the bioreactor compared to the total mass in the activated sludge system) was set at about 10%. It was found that the release of protein from the anaerobic bioreactor was greater than that from the aerobic bioreactor. The SOUR data suggested that the released protein from the anaerobic bioreactor was easily degraded when the sludge was returned to the activated sludge system. It was also found that when the proportion of sludge added to the anaerobic bioreactor in batch tests was approximately 10%, the protein release was about 30 mg/L. When the proportion of sludge added was increased to 26 to 41%, the release was reduced to 10 and 6 mg/L, respectively. Within 30 hours, the protein release was complete. This suggests that there is an optimum or maximum amount of recycle or interchange (~10%) for the process to function best. / Master of Science

Food waste is a desirable feedstock for anaerobic digestion because it is high in moisture and is an easily degradable material. However, mono-digestion of food waste often fails due to the accumulation of volatile fatty acids. Supplementing trace elements is one strategy to combat this issue. This study examined the effect of supplementing trace elements (iron, nickel, selenium, molybdenum, magnesium, zinc, calcium, copper, manganese, cobalt) on the methane yield and organic waste destruction of anaerobically digested food waste. Methane yield of food waste with and without the inorganic salt trace element was determined by the gas density-based biomethane potential method at mesophilic (37°C) conditions over 30 days. The three treatments were inoculum only, food waste and inoculum, and food waste and inoculum with an added trace element solution. There was no significant difference between treatments in terms of waste stabilization (percent volatile solids, total solids, and total chemical oxygen demand reduction) between treatments. The average cumulative biogas produced was 41% higher, and the average total cumulative methane produced was 23% higher in the treatment with the trace element supplement. Mean methane yield was not different (p > 0.05) between treatments over the 30 days, and there was no difference (p > 0.05) in biomethane potential between treatments. In addition, greenhouse gas reduction potential was estimated from food waste streams in Montgomery, VA using anaerobic digestion. The purpose of this work was to (1) estimate the total mass of food waste produced in Montgomery, VA in a year, (2) use the results from the biomethane potential analyses to inform the sizing of a theoretical community digester in Montgomery, VA, and (3) estimate the greenhouse gas reduction potential of anaerobically digesting the food waste instead of sending it to landfill. Greenhouse gas reduction was calculated using the Climate Action Reserve Organic Waste Digestion Project Protocol guidelines. The greenhouse gas reduction potential was estimated as 6,532 tonnes of carbon dioxide equivalent per year (tCO2e/year), with approximately 693 m3 methane produced per day. In one year, the digester would generate an estimated 7370 kWh of energy which has the potential to power 149 homes for a year in Montgomery, VA. In addition, 4130 tonnes/year of composted digestate would be available as fertilizer for surrounding farms. / Master of Science / Currently, about one-third of the entire U.S. food supply is lost or wasted. A large portion of that food waste is sent to landfills, where it produces methane, a greenhouse gas. Instead, food waste can be broken down to produce biogas during anaerobic digestion. Anaerobic digestion is a process in which microorganisms break down organic materials in the absence of oxygen to produce biogas and digestate, a material used as a soil amendment or fertilizer. However, anaerobically digesting food waste often leads to process instability and failure due to a buildup of undesirable intermediates. Microorganisms in anaerobic digestion require certain trace elements (i.e., iron, copper) that food waste often lacks; therefore, supplementing key trace elements may improve the anaerobic digestion of food waste. This research aimed to assess the effect of supplementing key trace elements (iron, copper, zinc, calcium, magnesium, nickel, manganese, selenium, molybdenum, cobalt) on organic matter degradation and methane yield. Methane yield of food waste with and without the inorganic salt trace element was determined by the gas density-based biomethane potential method at mesophilic (37°C) conditions over 30 days. The average cumulative biogas produced was 41% higher, and the average total cumulative methane produced was 23% higher in the bottles containing a trace element supplement. No significant difference was seen in the two groups when comparing organic matter degradation. These results demonstrate that supplementing trace elements can improve biogas and methane production. Greenhouse gas reductions from anaerobically digesting food waste instead of sending it to landfills were determined for Montgomery, VA. The results from the biomethane potential test informed the design of a theoretical community digester. Greenhouse gas reduction was calculated using the Climate Action Reserve Organic Waste Digestion Project Protocol equations. The greenhouse gas reduction was determined as 6,532 tonnes of carbon dioxide equivalent per year (tCO2e/year). The digester would produce approximately 693 m3 methane/day, which has the potential to power 149 homes for a year in Montgomery, VA. In addition, 4130 tonnes/year of compost would be produced and available as a fertilizer for surrounding farms.

Land application of biosolids has been demonstrated to improve nutrient availability (mainly N and P) and improve organic matter in soils, but the effects of biosolids on C sequestration and N cycling in the Mid-Atlantic region is not well understood. The objectives were: 1) to investigate soil C sequestration at sites with a long-term history of biosolids either in repeated application or single large application; 2) to characterize and compare soil C chemistry using advanced 13C nuclear magnetic resonance (NMR) and C (1s) near edge x-ray absorption fine structure (NEXAFS) spectroscopic techniques; and 3) to compare biosolids types and tillage practices on short-term N availability in the Coastal Plain soils. Biosolids led to C accumulation in the soil surface (< 15 cm) after long-time application in both Piedmont and Coastal Plain soils. The C saturation phenomenon occurred in Coastal Plain soils, thus additional soil C accumulation was not achieved by increasing C inputs from biosolids to the Coastal Plain. Soil organic C from profiles in the field sites was not different at depths below the plow layer (15-60 cm). The quantitative NMR analyses concluded that O-alkyl C was the dominant form in the particulate organic matter (POM), followed by aromatic C, alkyl C, COO/N-C=O, aromatic C-O, OCH3 / NCH and ketones and aldehydes. The aliphatic C and aromatic C were enriched but the O-alkyl C was decreased in the biosolids-amended soils. The changes indicated that the biosolids-derived soil C was more decomposed and, thus, more stable than the control. The NEXAFS spectra showed that O-alkyl C was the dominant form in the POM extracted from biosolids-amended soils, followed by aromatic C, alkyl C, carboxylic C and phenolic C groups. These results were similar to those from NMR analysis. The regression and correlation analyses of C functional groups in the POM between NEXAFS and NMR indicated that both techniques had good sensitivity for the characterization of C from biosolids-amended soils. To evaluate short-term biosolids N availability, a three-year field study to investigate the effects of lime-stabilized (LS) and anaerobically digested (AD) biosolids on N availability in a corn-soybean rotation under conventional tillage and no-tillage practices was set up in 2009-2011. Results showed that both LS and AD biosolids increased spring soil nitrate N, plant tissue N at silking, post-season corn stalk nitrate N, grain yield, and soil total N by the end of the growing season. The same factors used to calculate plant available N for incorporated biosolids can be used on biosolids applied to no-till systems in coarse-textured soils. All these results indicated that the application of biosolids affects the long-term quantification and qualification of soil organic C and also improve short-term N availability in the Mid-Atlantic region. / Ph. D.

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

The primary purpose of this study is to understand the effects of wastewater sludge feed cations on volatile solids destruction, odor control, and dewaterability. The role of influent feed cations and addition of chemical coagulants to sludge were evaluated for those characteristics following anaerobic digestion. Wastewater sludge samples were obtained from seven municipal wastewater treatment plants. Subsequently, batch digestion of the sludges was performed anaerobically in the laboratory with 30 days of SRT. Conditioning with cationic polymer and dewatering simulating a high solids centrifuge were performed after digestion. It was found that volatile solids destruction and volatile organic sulfur compounds generation increased proportionally as iron content in influent increased. However, they decreased as aluminum content in influent increased. It was also found that as iron content in influent increased, higher optimum polymer dose was required for dewatering. On the contrary, increase in aluminum content in influent resulted in decrease in the amount of optimum polymer dose. Direct addition of iron to the digesting sludge can be the most efficient point of addition with respect to volatile solids destruction, odor control, and conditioning of digested sludge. / Master of Science

The objective of this research was to design an alternative wastewater treatment system for turkey processing plants to recover energy and reduce N and P to allowable discharge levels. The objective included: 1. Determine the quantity and quality of biogas produced from the turkey processing wastewater (TPW) and COD reduction efficiency. 2. Design a waste treatment system and validate proof of concept for simultaneous P and N removal with a goal of attaining effluent concentrations of 0.1 mg/L and 4 mg/L, for P and N, respectively. A lab-scale complete mixed anaerobic digester was used for turkey processing wastewater (TPW) digestion and biogas recovery running for 6 months. Along with the anaerobic digester, a two-sludge system called A2N-SBR consisting of an anaerobic-anoxic sequencing batch reactor and an attached growth post-nitrification reactor was added for biological nitrogen and phosphorus removal running for 3 months. Biogas production yields of 778 + 89 mL/gVSadded and 951.30 mL/g COD were obtained through anaerobic digestion. Also, an energy balance was conducted on a pilot scale digester for a turkey processing plant with wastewater production of 2160 m3/d and using a combined heat and power (CHP) enginefor conversion of biogas to heat and electricity. Although the biogas yield achieved in a complete mixed reactor was relatively lower than yields obtained in previous studies using reactors such as UASB, still a complete mixed reactor can be a good choice for biogas recovery from TPW and can be used for codigestion with some specific turkey processing byproducts for biogas recovery. Nitrogen and phosphorus removal in the A2N-SBR system were 47% and 75%, respectively, and during the study the nitrogen and phosphorus removal mean concentration in effluent did not meet the nutrient limits specified in the objectives. Average TP and TN in the effluent were 3.2 mg/L and 137 mg/L, respectively. Throughout the study, the nitrification reactor biofilm was not completely developed. Incomplete nitrification and poor settling might be the reasons that quality obtained in effluent was low. To improve the process condition in A2N-SBR, online monitoring of pH, dissolved oxygen (DO) and oxidation reduction potential (ORP) can help to optimize each stage in the SBR and stages duration can be set based on the results. / Master of Science