Graduation Year

2011

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Daniel H. Yeh

Keywords

Algal Biofuel, Anerobic biological treatment, Photobioreactor, Ultrafiltration, Water-Energy Nexus

Abstract

An innovative wastewater treatment technology was developed to recover renewable resources, such as water, energy and nutrients, from sewage. First, a novel synthetic sewage was evaluated for its suitability to serve as an alternative substrate for lab-scale wastewater treatment (WWT) research. Based on granular dried cat food, Complex Organic Particulate Artificial Sewage (COPAS) is a commercially-available, flexible, and easy to preserve feed. Characteristics of COPAS, namely chemical composition, disintegration/dissolution kinetics, and anaerobic biodegradability, were determined. Anaerobic bioassays indicate that COPAS is highly biodegradable at the concentration used to simulate household sewage (1000 mg/L), with more than 72% of the theoretical methane content reached after 30 d of incubation. Results indicate that COPAS is a suitable substrate as a surrogate of domestic sewage.

In the second stage of the research, a lab-scale, 10L gas-lift anaerobic membrane bioreactor (Gl-AnMBR) was designed, fabricated and tested. The AnMBR is a hybrid treatment technology that combines anaerobic biological treatment with low-pressure membrane filtration. Although AnMBR has been used in many instances for the treatment of high strength industrial or agricultural wastewater, relatively little has been reported about its application for the treatment of domestic sewage and further conversion and recovery of resources embedded in sewage, such as energy and nutrient enriched water. The 10L column reactor uses a tubular PVDF ultrafiltration membrane (with biogas as sparge gas) for sludge/water separation. COPAS was used as synthetic feed (at 1000 mg/L) to represent household wastewater. The configuration showed excellent removal efficiencies of organic matter (up to 98% and 95% in COD and TOC removal, respectively) while producing energy in the form of methane at quantities suitable for maintaining membrane scrubbing (4.5 L/d of biogas). Soluble nutrients were recovered in the effluent in the forms of NH4, (9.1±4.2 mg/L), NO3 (2.2±0.9 mg/L) and PO4 (20±7.13 mg/L). The energy footprint (net energy) of this reactor was evaluated and the energy requirements per volume of permeate produced was found to be in the range of -1.2 to 0.7 kWh/m3, depending on final conversion of methane to electric or thermal energy respectively. These values could potentially be improved towards energy surplus (-2.3 to -0.5 kWh/m3) if applied to plant scale operation, which would employ more efficient pumps than those used in the lab. Results from this study suggest that the Gl-AnMBR can be applied as a sustainable treatment tool for resource recovery from sewage, which can further be optimized for large scale operation.

In the final stage of this research, further resource recovery from sewage was investigated by coupling the Gl-AnMBR with an innovative gas-lift algal photo MBR (APMBR). To our knowledge, this is the first reported application of membranes (in particular gas-lift tubular) for separation of algal cells from effluent in a continuous-flow photobioreactor. Nutrient rich effluent (9 mg/L NH4-N and 20 mg/L PO4-P) from the Gl-AnMBR treating domestic wastewater was used as substrate to grow the biofuel producing microalgae Chlorella sorokiniana (Cs). The initial set of operational conditions tested in this study (HRT of 24 hours, operational flux of 4.5 LMH, air-lift flow rate (Qa) of 0.1 L/min and 0.1 bars of membrane inlet pressure), achieved 100% removal efficiencies for NH4 and PO4. Flux remained constant during the experimental period which demonstrated the efficacy of gas lift as a membrane fouling control strategy for an algae bioreactor. Because the algae is photoautotrophic, little removal of organic carbon was expected nor observed. Further studies are required to better understand the fate and cycling of carbon in the APMBR. Limited information is available in the literature regarding biofuel-producing, algal photo MBRs utilizing anaerobic effluents as feedstock, which makes this study an important step in understanding the design and performance of combined anaerobic/algal biotechnology for large scale application of wastewater resource recovery.

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