Simultaneous ammonium and phosphate recovery and stabilization from urban sewage sludge anaerobic digestates using reactive sorbents

Abstract

The use of low-cost inorganic sorbents as a new sustainable strategy to enhance the valorization of nutrients (N-P-K), from the urban water cycle (e.g., side streams from sewage sludge anaerobic digestion), in agriculture applications is presented. The simultaneous recovery and stabilization of ammonium and phosphate by using a mixture of two reactive sorbents (Na and K zeolites and magnesium oxide) was evaluated. The nutrients stabilization process, favoured at alkaline pH values, is carried out by a) the precipitation of phosphate ions with magnesium and/or ammonium ions and b) the sorption of ammonium by Na- and K-zeolites. MgO(s) promoted the stabilization of phosphate as bobierrite (Mg(PO)(s)) or struvite (MgNHPO(s)) depending on the applied dose. Doses with the stoichiometric molar ratio of Mg/P promote the formation of bobierrite, while molar ratios higher than 3 favour the formation of struvite. Na zeolites (NaP1-NA, NaP1-IQE) demonstrated efficiency on ammonium stabilization between 60±2 (for 15gZ/L) to 90±3% (for 50gZ/L). The ammonium recovery efficiency is limited by the zeolite sorption capacity. If the target of the fertilizing criteria should include K, then the use of a K-zeolite (e.g., 5AH-IQE) provides a good solution. The optimum pH for the precipitation of struvite and bobierrite is 9.5 and the optimum pH for ammonium removal is between 4 and 8.5. N is present in higher concentrations (up 0.7-1gNH/L) when pH is ranged between 8.2 and 8.6. The ammonium recovery ratios were better than those previously reported using only magnesium oxide or even a more expensive reagent as newberrite (MgHPO(s)). The recovery mechanisms described generate low-solubility stabilized nutrients forms that potentially can be applied as slow-release fertilizers in agriculture. Thus, the use in agriculture of blends of digested sludge with low-solubility stabilized nutrients forms will improve soils quality properties in terms of organic matter and nutrients availability.

Validated innovative approaches for energy-efficient resource recovery and re-use from municipal wastewater: From anaerobic treatment systems to a biorefinery concept

“…The recovered nutrients from WWTPs can be utilized for struvite and/or Ca-P precipitation (Cieślik and Konieczka 2017;Melia et al 2017) or biochar adsorption (Huggins et al 2016). Struvite (MgNH4PO4) crystallization has been successfully used for simultaneous recovery of nutrients from wastewater (Hermassi et al 2018) together with calcium phosphate (Ca3(PO4)2) (Le Corre et al 2009). Struvite is more preferred in agricultural use due to the fact that magnesium (Mg), N and P are released simultaneously (1:1:1 M ratio), and that the rate of nutrient release is slow compared to other fertilizers (Puchongkawarin et al 2015).…”

“…Several other benefits are also associated with P recovery by crystallization. For instance, the volume of the sludge produced together with other undesired precipitates diminishes, which eventually decreases the cost of sludge disposal (Hermassi et al 2018).…”

“…Potassium recovery from wastewater has not been substantially considered and is an emerging issue (Batstone et al 2015). There are also quite number of other promising nutrient recovery technologies that are yet invalidated, such as microbial recovery cell-anaerobic osmotic membrane bioreactor ((MRC)-AnOMBR system (Hou et al 2017), reactive sorbents (Hermassi et al 2018) and microalgae (Viruela et al 2016).…”

“…The key factors that influence the application of post-sorbent fertilizers are the availability of feedstock, the technology to manufacture fertilizers, and the investment costs and capacity. (Hermassi et al 2018). In addition, soil measurements together with plant bioavailability indices can help to determine fertilizer performance (Peng et al 2018).…”

Groundwater Treatment using a Solid Polymer Electrolyte Cell with Mesh Electrodes

“…Before the EO treatments in the SPE cells, the groundwater sample was conveniently softened by adding 20 g L −1 of a Na + ‐zeolite (NaP1‐NA), synthesized by a hydrothermal method from coal combustion fly ash (CFA) . The properties of this material have been well characterized in earlier work . Softening was completed upon vigorous magnetic stirring at 1100 rpm for 24 h, at room temperature.…”