Nutrient recovery from wastewater: A review on the integrated Physicochemical technologies of ammonia stripping, adsorption and struvite precipitation

Abstract

• A review on technical integration for N-P-K recovery was performed. • “Stripping → K-struvite precipitation” can recover N, P and K simultaneously. • Crystal size should be enlarged for upscaling “stripping + struvite precipitation”. • (Modified-)biochar/zeolite have been used as the seed of struvite or adsorbent. • Adsorbent could replace sulfuric acid in acid scrubber following stripping column. The field of wastewater management has seen a transition from “contaminant removal” in wastewater treatment plants (WWTPs) to “nutrient recovery” in so-called water resource recovery facilities (WRRFs) for years. For achieving a higher efficiency and economic benefits, the integration of multiple nutrient recovery technologies (NRTs) is of increased interest. This study provides a comprehensive overview of the integration of ammonia stripping, adsorption and struvite precipitation, three of the most dominant physicochemical NRTs. In their different combinations, a critical comparison of the available research is given from the perspective of process technical description, the current scale of application and potential challenges and perspectives ahead. The integration between ammonia stripping and struvite precipitation has been applied in either “one single integrated reactor” at lab scale or “multiple discrete reactors” at pilot/full scale. The collection of struvite should be further optimized, and “stripping → K-struvite precipitation” is expected to recover all of three macronutrients. In the technical integration between struvite precipitation and adsorption, small pristine adsorbents (<50 μm) have been used as the seeding material for struvite, while pristine and surface-modified adsorbents have been integrated with struvite precipitation as the sorbent material. Some magnesium-modified adsorbents achieved a higher removal efficiency and adsorption capacity than pristine adsorbent. The non-preferential adsorption is one of the main challenges limiting its upscaling. Lastly, stripping has been applied in the regeneration process of zeolite. Its economic benefits should be further analysed before its upscaling. This review proposed to apply adsorbents as the alternative of sulfuric acid in the acid scrubber following the stripping column. This new perspective may decrease the cost on ammonia stripping.