Cynthia Castro | University of Massachusetts Amherst (original) (raw)

Papers by Cynthia Castro

Journal of Water Sanitation and Hygiene for Development, Aug 18, 2014

A microbial fuel cell (MFC) latrine that treats human waste and produces compost and electricity ... more A microbial fuel cell (MFC) latrine that treats human waste and produces compost and electricity was deployed in Agona Nyakrom, Ghana. After solid wastes were composted, the MFC treated organic matter and nitrogen from the remaining liquid stream. Organic matter was oxidized in the anode by anode-respiring bacteria that transfer electrons to an external circuit, producing electricity, which was observed to be 268 nW/m 2 after two years of operation. A separate nitrification stage transformed ammonium present in urine, to nitrate. Nitrate was reduced to nitrogen gas by cathodeoxidizing bacteria in the cathode completing nitrogen removal. The MFC latrine was constructed onsite using local labor and materials. Evidence of total nitrogen removal and power production was observed while the MFC latrine was in operation. Multiple user challenges and maintenance affected the performance, yielding low power output. The initial findings suggest that the viability of the system is directly correlated with its use. Incorporating the MFC latrine system into the user community's typical social practices is key to a successful deployment of the MFC latrine as a sanitation technology.

Influence of environmental stress on the microalgal-bacterial process during nitrogen removal

Journal of Environmental Management, 2021

Globally, there is a dire need for a new class of advanced non-sewered sanitation systems (NSSS) ... more Globally, there is a dire need for a new class of advanced non-sewered sanitation systems (NSSS) to provide onsite wastewater treatment that is capable of meeting stringent discharge or reuse criteria. These systems need to be simple to operate and maintain, reliable, and resilient to unreliable electrical service. The NEWgenerator (NG) is a compact, automated, solar-powered wastewater treatment system comprised of three major treatment processes: anaerobic membrane bioreactor (AnMBR), nutrient capture system (NCS) with ion exchange and carbon sorption, and electrochlorination (EC). The NG system operated at an informal settlement community in South Africa over a 534 d period, treating high-strength blackwater (BW) and yellow water (YW) from a public toilet facility. Over three test stages (BW, BW + YW, BW) that included several periods of dormancy, the NG system was able to provide a high level of removal of total suspended solids (97.6 ± 3.1%), chemical oxygen demand (94.5 ± 5.0%), turbidity (96.3 ± 9.7%), color (92.0 ± 10.5%), total nitrogen (82.1 ± 24.0%), total phosphorus (43.0 ± 22.1%), E. coli (7.4 ± 1.5 LRV, not detected in effluent), and helminth ova (not detected in effluent). The treatment levels met most of the ISO 30500 NSSS standard for liquid effluent and local water reuse criteria. A series of maintenance events were successfully conducted onsite over the 534 d field trial: two membrane cleanings, two NCS regenerations, and granular activated carbon replacement. Desludging, a major pain point for onsite sanitation systems, was unnecessary during the field trial and thereby not performed. The AnMBR performed well, removing 94.5 ± 5.0% of the influent COD across all three stages. The high COD removal rate is attributed to the sub-micron separation provided by the ultrafiltration membrane. The NCS was highly efficient at removing total nitrogen, residual COD and color, but the regeneration process was lengthy and is a topic of ongoing research. The EC provided effective disinfection, but frequent prolonged run cycles due to power supply and water quality issues upstream limited the overall system hydraulic throughput. This extended field trial under actual ambient conditions successfully demonstrated the feasibility of using advanced NSSS to address the global water and sanitation crises.

Science of The Total Environment, 2021

• 1.5 yr field trial of a zeolite-based nutrient capture system for ammonium removal. • Three amm... more • 1.5 yr field trial of a zeolite-based nutrient capture system for ammonium removal. • Three ammonium loading cycles of 291, 110, and 52 days were evaluated. • Ammonium removal achieved for each cycle was 80 ± 28%, 64 ± 23%, and 94 ± 11%. • Two onsite regenerations were conducted between cycles. • Regeneration efficiencies for each regeneration were 76 ± 0.7% and 96 ± 1.0%.

Journal of Water Sanitation and Hygiene for Development, Oct 21, 2016

Biological electrochemical systems (BESs) have the potential for decentralized treatment in devel... more Biological electrochemical systems (BESs) have the potential for decentralized treatment in developing countries. A 46 L, two-chamber, hydraulically partitioned microbial fuel cell (MFC) was designed to replicate low-flow scenarios leaving a composting toilet. The co-evolution of electricity and methane in this MFC was evaluated by testing two distinct waste streams: synthetic feces (Case F) and municipal primary effluent (Case W). Oxidation of organic matter was 76 ± 24% during Case F and 67 ± 21% during Case W. Methanogenesis was dominant in the anode, yielding potential power of 3.3 ± 0.64 W/m 3 during Case F and 0.40 ± 0.07 W/m 3 during Case W. Electrical power production was marginal, Case F ¼ 4.7 ± 0.46 and Case W ¼ 10.6 ± 0.39 μW/m 3 , although potentially useful in energy-limited areas. Complimentary batch cultivations with anode inocula yielded greater methane production in the presence of graphite. 74 ± 11% more methane was produced with graphite than suspended growth enrichments and 58 ± 10% more than enrichments with non-conductive plastic beads. The co-production of methane and electricity in an MFC may have utility in decentralized treatment. Further work is needed to optimize power from both electricity and methane.

Environmental Science: Water Research & Technology

Clinoptilolite zeolite was chemically modified with sodium, calcium, or magnesium to comparativel... more Clinoptilolite zeolite was chemically modified with sodium, calcium, or magnesium to comparatively study the physical recovery of ammonium and phosphates from simulated blackwater.

Achieving safely managed sanitation and resource recovery in areas that are rural, geographically... more Achieving safely managed sanitation and resource recovery in areas that are rural, geographically challenged, or experiencing rapidly increasing population density may not be feasible with centralized facilities due to space requirements, site-specific concerns, and high costs of sewer installation. Non-sewered sanitation (NSS) systems have the potential to provide safely managed sanitation and achieve strict wastewater treatment standards. One such NSS treatment (backend) technology is the NEWgeneratorTM, which includes an anaerobic membrane bioreactor (AnMBR), nutrient recovery via ion exchange, and electrochlorination. Although the system has been shown to achieve robust treatment of real waste streams for over 100 users, the technology’s relative life cycle sustainability across deployment locations remains unclear. This study characterizes the financial viability and life cycle environmental impacts of the NEWgeneratorTM and prioritizes opportunities to advance system sustainab...

Water

Bioelectrochemical systems with denitrifying biocathodes have been of interest for the removal of... more Bioelectrochemical systems with denitrifying biocathodes have been of interest for the removal of nitrate in decentralized wastewater treatment applications. Only a few studies have directly focused on this application, but the removal rates have been very low. This study evaluated the operational parameters that affect the nitrate removal of two-chambered microbial fuel cells (MFCs) with a biocathode, particularly, the carbon to nitrogen ratio (C:N) and proton diffusivity across electrode chambers. The results show that proton diffusion across a proton exchange membrane is not a limiting step in nitrogen removal performance. At C:N ratios of 4 and 8, biocathodes with a continuously supplied carbon source at the anode were able to achieve complete nitrogen removal at a rate of 0.97 ± 0.21 and 1.15 ± 0.13 mg N L−1 d−1, respectively. However, as the C:N ratio increased from 4, 8, 16, and 32, the electrode potentials decreased accordingly. Ratio 4 C:N had a cathodic reduction potential...

Proceedings of the Water Environment Federation, 2012

The goal of the dissertation is the investigation of financial risk analysis methodologies, using... more The goal of the dissertation is the investigation of financial risk analysis methodologies, using the schemes for extreme value modeling as well as techniques from copula modeling. Extreme value theory is concerned with probabilistic and statistical questions re- lated to unusual behavior or rare events. The subject has a rich mathematical theory and also a long tradition of applications in a variety of areas. We are interested in its application in risk management, with a focus on estimating and forcasting the Value-at-Risk of financial time series data. Extremal data are inherently scarce, thus making inference challenging. In order to obtain good estimates for risk measures, we develop a two-stage approach: (1) fitting the GARCH-type models at the first stage to describe the volatility clustering and other stylized facts of financial time series; (2) using the extreme value theory based models to fit to the tails of the residuals. Additionally, the performance measures provide in...

iii LIST OF TABLES vii LIST OF FIGURES viii Chapter 1: Sanitation in the Developing World 1 1.

Journal of Water, Sanitation and Hygiene for Development, 2014

A microbial fuel cell (MFC) latrine that treats human waste and produces compost and electricity ... more A microbial fuel cell (MFC) latrine that treats human waste and produces compost and electricity was deployed in Agona Nyakrom, Ghana. After solid wastes were composted, the MFC treated organic matter and nitrogen from the remaining liquid stream. Organic matter was oxidized in the anode by anode-respiring bacteria that transfer electrons to an external circuit, producing electricity, which was observed to be 268 nW/m2 after two years of operation. A separate nitrification stage transformed ammonium present in urine, to nitrate. Nitrate was reduced to nitrogen gas by cathode-oxidizing bacteria in the cathode completing nitrogen removal. The MFC Latrine was constructed on-site using local labor and materials. Evidence of total nitrogen removal and power production was observed while the MFC Latrine was in operation. Multiple user challenges and maintenance affected the performance, yielding low power output. The initial findings suggest that the viability of the system is directly co...

Journal of Water, Sanitation and Hygiene for Development, 2014

Proceedings of the Water Environment Federation, 2012

Journal of Water Sanitation and Hygiene for Development, Aug 18, 2014

A microbial fuel cell (MFC) latrine that treats human waste and produces compost and electricity ... more A microbial fuel cell (MFC) latrine that treats human waste and produces compost and electricity was deployed in Agona Nyakrom, Ghana. After solid wastes were composted, the MFC treated organic matter and nitrogen from the remaining liquid stream. Organic matter was oxidized in the anode by anode-respiring bacteria that transfer electrons to an external circuit, producing electricity, which was observed to be 268 nW/m 2 after two years of operation. A separate nitrification stage transformed ammonium present in urine, to nitrate. Nitrate was reduced to nitrogen gas by cathodeoxidizing bacteria in the cathode completing nitrogen removal. The MFC latrine was constructed onsite using local labor and materials. Evidence of total nitrogen removal and power production was observed while the MFC latrine was in operation. Multiple user challenges and maintenance affected the performance, yielding low power output. The initial findings suggest that the viability of the system is directly correlated with its use. Incorporating the MFC latrine system into the user community's typical social practices is key to a successful deployment of the MFC latrine as a sanitation technology.

Influence of environmental stress on the microalgal-bacterial process during nitrogen removal

Journal of Environmental Management, 2021

Globally, there is a dire need for a new class of advanced non-sewered sanitation systems (NSSS) ... more Globally, there is a dire need for a new class of advanced non-sewered sanitation systems (NSSS) to provide onsite wastewater treatment that is capable of meeting stringent discharge or reuse criteria. These systems need to be simple to operate and maintain, reliable, and resilient to unreliable electrical service. The NEWgenerator (NG) is a compact, automated, solar-powered wastewater treatment system comprised of three major treatment processes: anaerobic membrane bioreactor (AnMBR), nutrient capture system (NCS) with ion exchange and carbon sorption, and electrochlorination (EC). The NG system operated at an informal settlement community in South Africa over a 534 d period, treating high-strength blackwater (BW) and yellow water (YW) from a public toilet facility. Over three test stages (BW, BW + YW, BW) that included several periods of dormancy, the NG system was able to provide a high level of removal of total suspended solids (97.6 ± 3.1%), chemical oxygen demand (94.5 ± 5.0%), turbidity (96.3 ± 9.7%), color (92.0 ± 10.5%), total nitrogen (82.1 ± 24.0%), total phosphorus (43.0 ± 22.1%), E. coli (7.4 ± 1.5 LRV, not detected in effluent), and helminth ova (not detected in effluent). The treatment levels met most of the ISO 30500 NSSS standard for liquid effluent and local water reuse criteria. A series of maintenance events were successfully conducted onsite over the 534 d field trial: two membrane cleanings, two NCS regenerations, and granular activated carbon replacement. Desludging, a major pain point for onsite sanitation systems, was unnecessary during the field trial and thereby not performed. The AnMBR performed well, removing 94.5 ± 5.0% of the influent COD across all three stages. The high COD removal rate is attributed to the sub-micron separation provided by the ultrafiltration membrane. The NCS was highly efficient at removing total nitrogen, residual COD and color, but the regeneration process was lengthy and is a topic of ongoing research. The EC provided effective disinfection, but frequent prolonged run cycles due to power supply and water quality issues upstream limited the overall system hydraulic throughput. This extended field trial under actual ambient conditions successfully demonstrated the feasibility of using advanced NSSS to address the global water and sanitation crises.

Science of The Total Environment, 2021

• 1.5 yr field trial of a zeolite-based nutrient capture system for ammonium removal. • Three amm... more • 1.5 yr field trial of a zeolite-based nutrient capture system for ammonium removal. • Three ammonium loading cycles of 291, 110, and 52 days were evaluated. • Ammonium removal achieved for each cycle was 80 ± 28%, 64 ± 23%, and 94 ± 11%. • Two onsite regenerations were conducted between cycles. • Regeneration efficiencies for each regeneration were 76 ± 0.7% and 96 ± 1.0%.

Journal of Water Sanitation and Hygiene for Development, Oct 21, 2016

Biological electrochemical systems (BESs) have the potential for decentralized treatment in devel... more Biological electrochemical systems (BESs) have the potential for decentralized treatment in developing countries. A 46 L, two-chamber, hydraulically partitioned microbial fuel cell (MFC) was designed to replicate low-flow scenarios leaving a composting toilet. The co-evolution of electricity and methane in this MFC was evaluated by testing two distinct waste streams: synthetic feces (Case F) and municipal primary effluent (Case W). Oxidation of organic matter was 76 ± 24% during Case F and 67 ± 21% during Case W. Methanogenesis was dominant in the anode, yielding potential power of 3.3 ± 0.64 W/m 3 during Case F and 0.40 ± 0.07 W/m 3 during Case W. Electrical power production was marginal, Case F ¼ 4.7 ± 0.46 and Case W ¼ 10.6 ± 0.39 μW/m 3 , although potentially useful in energy-limited areas. Complimentary batch cultivations with anode inocula yielded greater methane production in the presence of graphite. 74 ± 11% more methane was produced with graphite than suspended growth enrichments and 58 ± 10% more than enrichments with non-conductive plastic beads. The co-production of methane and electricity in an MFC may have utility in decentralized treatment. Further work is needed to optimize power from both electricity and methane.

Environmental Science: Water Research & Technology

Clinoptilolite zeolite was chemically modified with sodium, calcium, or magnesium to comparativel... more Clinoptilolite zeolite was chemically modified with sodium, calcium, or magnesium to comparatively study the physical recovery of ammonium and phosphates from simulated blackwater.

Achieving safely managed sanitation and resource recovery in areas that are rural, geographically... more Achieving safely managed sanitation and resource recovery in areas that are rural, geographically challenged, or experiencing rapidly increasing population density may not be feasible with centralized facilities due to space requirements, site-specific concerns, and high costs of sewer installation. Non-sewered sanitation (NSS) systems have the potential to provide safely managed sanitation and achieve strict wastewater treatment standards. One such NSS treatment (backend) technology is the NEWgeneratorTM, which includes an anaerobic membrane bioreactor (AnMBR), nutrient recovery via ion exchange, and electrochlorination. Although the system has been shown to achieve robust treatment of real waste streams for over 100 users, the technology’s relative life cycle sustainability across deployment locations remains unclear. This study characterizes the financial viability and life cycle environmental impacts of the NEWgeneratorTM and prioritizes opportunities to advance system sustainab...

Water

Bioelectrochemical systems with denitrifying biocathodes have been of interest for the removal of... more Bioelectrochemical systems with denitrifying biocathodes have been of interest for the removal of nitrate in decentralized wastewater treatment applications. Only a few studies have directly focused on this application, but the removal rates have been very low. This study evaluated the operational parameters that affect the nitrate removal of two-chambered microbial fuel cells (MFCs) with a biocathode, particularly, the carbon to nitrogen ratio (C:N) and proton diffusivity across electrode chambers. The results show that proton diffusion across a proton exchange membrane is not a limiting step in nitrogen removal performance. At C:N ratios of 4 and 8, biocathodes with a continuously supplied carbon source at the anode were able to achieve complete nitrogen removal at a rate of 0.97 ± 0.21 and 1.15 ± 0.13 mg N L−1 d−1, respectively. However, as the C:N ratio increased from 4, 8, 16, and 32, the electrode potentials decreased accordingly. Ratio 4 C:N had a cathodic reduction potential...

Proceedings of the Water Environment Federation, 2012

The goal of the dissertation is the investigation of financial risk analysis methodologies, using... more The goal of the dissertation is the investigation of financial risk analysis methodologies, using the schemes for extreme value modeling as well as techniques from copula modeling. Extreme value theory is concerned with probabilistic and statistical questions re- lated to unusual behavior or rare events. The subject has a rich mathematical theory and also a long tradition of applications in a variety of areas. We are interested in its application in risk management, with a focus on estimating and forcasting the Value-at-Risk of financial time series data. Extremal data are inherently scarce, thus making inference challenging. In order to obtain good estimates for risk measures, we develop a two-stage approach: (1) fitting the GARCH-type models at the first stage to describe the volatility clustering and other stylized facts of financial time series; (2) using the extreme value theory based models to fit to the tails of the residuals. Additionally, the performance measures provide in...

iii LIST OF TABLES vii LIST OF FIGURES viii Chapter 1: Sanitation in the Developing World 1 1.

Journal of Water, Sanitation and Hygiene for Development, 2014

A microbial fuel cell (MFC) latrine that treats human waste and produces compost and electricity ... more A microbial fuel cell (MFC) latrine that treats human waste and produces compost and electricity was deployed in Agona Nyakrom, Ghana. After solid wastes were composted, the MFC treated organic matter and nitrogen from the remaining liquid stream. Organic matter was oxidized in the anode by anode-respiring bacteria that transfer electrons to an external circuit, producing electricity, which was observed to be 268 nW/m2 after two years of operation. A separate nitrification stage transformed ammonium present in urine, to nitrate. Nitrate was reduced to nitrogen gas by cathode-oxidizing bacteria in the cathode completing nitrogen removal. The MFC Latrine was constructed on-site using local labor and materials. Evidence of total nitrogen removal and power production was observed while the MFC Latrine was in operation. Multiple user challenges and maintenance affected the performance, yielding low power output. The initial findings suggest that the viability of the system is directly co...

Journal of Water, Sanitation and Hygiene for Development, 2014

Proceedings of the Water Environment Federation, 2012