By Marcus Gay, NM WRRI Student Program Coordinator
Isuru Sachitra Abeysiriwardana Arachchige is a doctoral candidate at New Mexico State University’s (NMSU) Civil Engineering Department who is hoping to graduate next year with a PhD in Environmental Engineering. In 2019, Isuru was awarded an NM WRRI Student Water Research Grant for his project entitled, Anaerobic Digester Supernatant Treatment Using Algal Systems. Isuru’s research focuses on enhancing the performance of an integrated algal system that can recover energy, water, and nutrients from wastewater.
Publicly owned sewage treatment plants use technologies designed to breakdown pollutants in wastewater, and therefore maintain the public health and quality of surface water across the United States. However, the treatment technologies used at many of these plants require huge amounts of energy. Over the last few decades, algal-based technologies began emerging as a sustainable alternative to current wastewater treatment.
Typical domestic wastewater treatment plants use a process, called aerobic activated sludge, for removing dissolved organics from wastewater up to the water quality standard required for discharging. As a way of offsetting a portion of this high energy process, a practice used in medium to large-sized plants called anaerobic digestion of waste sludge could help recover about a quarter to half of the energy spent on the activated sludge process.
Currently, the nitrogen-rich supernatant resulting from anaerobic digestion is returned to the headworks of the treatment plant. This practice, however, increases the nitrogen load to the plant, thereby increasing the overall cost of treatment and limiting plant capacity. In response to this issue, researchers have proposed systems such as anammox-based processes to treat anaerobic digestion supernatant prior to recycling it to the headwork. However, most of these novel processes dissipate the valuable forms of nitrogen in the anaerobic digestion supernatant as gaseous nitrogen without any recovery.
Faculty and graduate students at NMSU have developed a novel algal wastewater treatment system which uses a species of algae that can remove and recover organic carbon and nutrients from domestic wastewater for beneficial reuse. With support from the NM WRRI Student Water Research Grant, Isuru, and the team of NMSU faculty and graduate students working on the project, intend to utilize these algal systems to treat the anaerobic digestion supernatant.
Isuru and his colleagues hypothesize that discharge-ready effluent can be produced by feeding anaerobic digestion supernatant blended with primary effluent to the algal system while generating biomass for nutrient and energy recovery. As Isuru explains, “If this technology can be proven for anaerobic digestion supernatant treatment through long-term studies, wastewater treatment plants in cities like Las Cruces with anaerobic digestion will have the opportunity to lower their operational cost by using this algal system while also generating an extra income through nutrient recovery.”
Isuru’s background in wastewater treatment started when he earned a degree in Civil Engineering from the University of Peradeniya in his home country of Sri Lanka in 2016. During his undergraduate program, he studied using sequencing batch reactors for dairy wastewater treatment. In 2017, he enrolled in the Environmental Engineering program at NMSU where he started his work on algal wastewater treatment systems. After he earned his Master of Science degree in 2018, Isuru started his PhD program at NMSU under the guidance of his faculty advisor, Dr. Nagamany Nirmalakhandan. In the future, Isuru hopes to work in industry or academia as a water and wastewater expert.