Recovery of Phosphorus from Waste Water Profiting from Biological Nitrogen Treatment: Upstream, Concomitant or Downstream Precipitation Alternatives

Abstract

Mined phosphate rock is the largest source of phosphorus (P) for use in agriculture and agro-industry, but it also is a finite resource irregularly distributed around the world. Alternatively, waste water is a renewable source of P, available at the local scale. In waste water treatment, biological nitrogen (N) removal is applied according to a wide range of variants targeting the abatement of the ammonium content. Ammonium oxidation to nitrate can also be considered to mitigate ammonia emission, while enabling N recovery. This review focuses on the analysis of alternatives for coupling biological N treatment and phosphate precipitation when treating waste water in view of producing P-rich materials easily usable as fertilisers. Phosphate precipitation can be applied before (upstream configuration), together with (concomitant configuration), and after (downstream configuration) N treatment; i.e., chemically induced as a conditioning pre-treatment, biologically induced inside the reactor, and chemically induced as a refining post-treatment. Characteristics of the recovered products differ significantly depending on the case studied. Currently, precipitated phosphate salts are not typified in the European fertiliser regulation, and this fact limits marketability. Nonetheless, this topic is in progress. The potential requirements to be complied by these materials to be covered by the regulation are overviewed. The insights given will help in identifying enhanced integrated approaches for waste water treatment, pointing out significant needs for subsequent agronomic valorisation of the recovered phosphate salts, according to the paradigms of the circular economy, sustainability, and environmental protection.

Use of Recovered Struvite and Ammonium Nitrate in Fertigation in Tomato (Lycopersicum esculentum) Production for boosting Circular and Sustainable Horticulture

“…P-recovered products used in this study were recovered by Århusvand A/S company (Denmark) and Murcia Este WWTP (Spain) in 2019 and 2020, respectively, through P-elutriation at full-scale followed by a crystallization unit from the sludge line. These samples were identified as highly pure struvite and accomplish the new legislative requirements for precipitated phosphate salts in the revised fertilizer directive [4] (Table S1). Moreover, N, P, and Mg 2+ content of struvite are close to the theoretical values (Table 2), within the range detected in a systemic comparison of commercially produced struvite [26], and accomplish for the prescription of the current legislation being the P content higher than 7% of the dry matter (DM).…”

“…The production of renewable and high-quality fertilizers from waste streams should be promoted, and the products should be tested in field conditions in order to boost circularity in horticulture systems. Among the most important recovering processes, the precipitation of P as struvite (MgNH 4 PO 4 •6H 2 O) should be highlighted [3,4]; in the last years, the production of ammonium nitrate (AN) (or ammonium sulphate) from WWTPs through liquid-liquid membrane contactors (LLMC), where N is captured into an acid, has also been investigated [5].…”

Synthesis and Characterization of 2D Magnesium Oxide Nanoflakes: A Potential Nanomaterial for Effective Phosphate Removal from Wastewater

“…It could be easily applied for phosphate removal on small-scale treatment facilities or wastewater with relatively low phosphate concentrations. [22] There are various factors that affect adsorption such as adsorbent particle dose and size, pH value, initial solute concentration, temperature, etc. [23,24] Various adsorbents have been examined, including zero-valent iron, [25] activated carbon, [26,27] aluminum oxide/hydroxide, [28,29] goethite, [30] calcite, [31] zeolite, [32] red mud, [33] and fly ash.…”

Hydroxyapatite Formation in a Single-Stage Anammox-Based Batch Treatment System: Reactor Performance, Phosphorus Recovery, and Microbial Community

“…Broadly, in view of biological treatment, phosphate precipitation can be accomplished according to upstream, concomitant, or downstream strategies. 6 Regarding the product finally obtained, magnesium phosphates (MgP) such as struvite (magnesium ammonium phosphate (MAP)) are frequently considered as an efficient slow-release fertilizer for crops, 7 whereas calcium phosphates (CaP) such as hydroxyapatite (HAP) offer broader industrial applications beyond fertilizers since the composition is similar to mined phosphate rock. 8 The equation for the crystallization of HAP (Ca 10 (PO 4 ) 6 (OH) 2 ), a mineral containing 18.5 wt % P, is as follows: (eq 1) 9 10Ca 6PO 2OH Ca (PO ) (OH) Owing to the significant enhancement in the energy balance achievable with respect to other conventional biotechnologies, completely autotrophic nitrogen (N) removal (i.e., the partial nitritation−anammox (PNA) process) is an appealing alternative for treating the N-rich sidestream centrates produced in urban WWTPs.…”