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1. Hybrid algal photosynthesis and ion-exchange (HAPIX) process for anaerobic digester centrate treatment

   Wang, M.; Payne, K.; Tong, S.; Zalivina, N.; Ergas, S.J. (March 2017, 1st IWA Conference on Algal Technologies for Wastewater Treatment)

   Algae-based wastewater treatment systems have the potential to reduce the energy cost of wastewater treatment processes by utilizing solar energy for biomass growth and nutrient removal. NH4+-N concentrations as high as 200- 300 mg/L are known to inhibit algae growth. Many research studies on the treatment of centrate after anaerobic digestion have been published recently. However, in these studies the centrate was diluted for the growth of algae due to the high NH4+-N concentrations, which are toxic to algae. Alternative solutions are necessary to treat high NH4+-N strength wastewater without addition of freshwater. Zeolites are natural hydrated aluminosilicate minerals that have been used to reduce ammonium inhibition on microorganisms due to their high affinity for ammonium ions. It is possible to use the ion-exchange (IX) capacity of zeolite to reduce the toxicity of ammonia to algae. Importantly, the zeolite, which becomes saturated with ammonium, can be reused as a slow release fertilizer. The objectives of this research were to evaluate the impact of zeolite dosage on the nutrient removal efficiency for high strength wastewater and develop mathematical models to predict the performance of hybrid IX and algae growth systems with varying doses of zeolite. 

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2. Hybrid Ion Exchange and Algae for High Strength Sidestream Wastewater Treatment

   Wang, M.; Payne, K.; Tong, S.; Ergas, S.J. (June 2017, WEF 2017 Nutrient Symposium)

   A hybrid ion-exchange and algae photosynthesis (HAPIX) process was used for treatment of side stream centrate from an anaerobic digester treating waste activated sludge. Although the high NH4+ -N concentration of the centrate (~1180 mg/L) inhibited the algae growth in unamended controls, addition of 150 g/L of zeolite reduced the ammonia toxicity due to its ion exchange capacity. NH4+-N was reduced from 1,180 mg/L to 107 mg/L within 24 hours by ion exchange. Na+ was the major cation exchanged with NH4+. The addition of algae further reduced the NH4+-N concentration to 10.5 mg/L after 8 days of operation. Zeolite that was saturated with NH4+ can be bioregenerated by the algae growth so that the zeolite can adsorb more NH4+ in the wastewater. The mathematical model that combined ion-exchange and algal photosynthesis processes predicted the aqueous NH4 + -N concentration well. The HAPIX process is feasible to treat high NH4+-N side stream wastewater. 

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3. Prospective Life Cycle Assessment and Cost Analysis of Novel Electrochemical Struvite Recovery in a U.S. Wastewater Treatment Plant

   https://doi.org/10.3390/su142013657  

   Morrissey, Karla G.; English, Leah; Thoma, Greg; Popp, Jennie (October 2022, Sustainability)

   Nutrient recovery in domestic wastewater treatment has increasingly become an important area of study as the supply of non-renewable phosphorus decreases. Recent bench-scale trials indicate that co-generation of struvite and hydrogen using electrochemical methods may offer an alternative to existing recovery options utilized by municipal wastewater treatment facilities. However, implementation has yet to be explored at plant-scale. In the development of novel nutrient recovery processes, both economic and environmental assessments are necessary to guide research and their design. The aim of this study was to conduct a prospective life cycle assessment and cost analysis of a new electrochemical struvite recovery technology that utilizes a sacrificial magnesium anode to precipitate struvite and generate hydrogen gas. This technology was modeled using process simulation software GPS-X and CapdetWorks assuming its integration in a full-scale existing wastewater treatment plant with and without anaerobic digestion. Struvite recoveries of 18–33% were achieved when anaerobic digestion was included, with a break-even price of $6.03/kg struvite and $15.58/kg of hydrogen required to offset increased costs for recovery. Struvite recovery reduced aquatic eutrophication impacts as well as terrestrial acidification impacts. Tradeoffs between benefits from struvite and burdens from electrode manufacturing were found for several impact categories. 

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4. A hybrid algal photosynthesis and ion-exchange (HAPIX) process for side stream wastewater treatment: Experimental and modeling studies

   Wang, M.; Payne, K.; Tong, S.; Ergas, S.J. (September 2017, Water Environment Federation Technical Exhibition and Conference (WEFTEC 2017))

   A hybrid ion-exchange and algal photosynthesis (HAPIX) process was used for treatment of side stream centrate from an anaerobic digester treating waste activated sludge. Although the high NH4+-N concentration of the centrate (~1180 mg/L) inhibited algal growth in unamended controls, addition of zeolite reduced the ammonia toxicity due to its ion exchange capacity. Na+ was the major cation exchanged with NH4+. Growth of algae further reduced the NH4+-N concentrations. Different zeolite dosages (60, 150, and 250 g/L) resulted in different concentrations of NH4+-N in solution. Algae grown in lower zeolite dosage (60 g/L) had high protein contents. A mathematical model that combined ion-exchange and algal photosynthesis processes predicted the aqueous NH4+-N concentration well. The HAPIX process is feasible for treatment of high NH4+-N strength side stream wastewaters while regulating intracellular algal biomass contents by adjusting zeolite dosages. 

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5. Hybrid Adsorption and Biological Treatment Systems (HABiTS) for Enhanced Nitrogen Removal in Onsite Wastewater Treatment

   Rodriguez-Gonzalez, L.; Payne, K.; Anderson, D.; He, Q.; Prouty, C.; Garcia, L.; Trotz, M.; Ergas, S. (October 2018, 27th Caribbean Water and Wastewater Conference & Exhibition Proceedings)

   Twenty-five United Nations member states in the wider Caribbean region ratified the Cartagena Convention, which covers the marine environment of the Gulf of Mexico, the Caribbean Sea and some parts of the Atlantic Ocean. The Land-Based Sources and Activities protocol (LBS Protocol) of that convention addresses nutrient pollution from sewage discharges, agricultural runoff and other sources. Unfortunately, most Caribbean people use conventional onsite wastewater treatment systems (OWTs), especially septic systems. These systems fail to remove nitrogen effectively, posing a challenge for near shore environments. Passive biological nitrogen removal (BNR) processes have been developed for OWTs that rely on simple packed bed bioreactors, with little energy or chemical inputs and low operations and maintenance (O&M) requirements. This paper provides a case study from Florida on the partnerships and pathways for research to develop an innovative technology, Hybrid Adsorption and Biological Treatment System (HABiTS), for nitrogen reduction in OWTs. HABiTS combine ion exchange materials and BNR to remove nitrogen from septic tank effluent and buffer transient loadings. HABiTS, employs natural zeolite material (e.g. clinoptilolite) and expanded clay in the first stage to achieve both ammonium ion exchange and nitrification. The second stage of HABiTS utilizes tire chips, elemental sulphur pellets and oyster shells for adsorption of nitrate as well as sulphur oxidizing denitrification. Under transient load applications, the nitrogen in excess of the biodegradation capacity during high loading events was partially retained within the ion exchange and adsorption materials and readily available later for the microorganisms during lower loading events. Results from a bench scale bioreactor study with marine wastewater, which is relevant to where seawater is used for toilet flushing, are also presented. Pilot scale tests on the OWT of an engaged stakeholder dependent on the marine environment, would contribute to broader discussions for paradigm shifts for nutrient removal from wastewater. 

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