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

M Hermassi; J Dosta; C Valderrama; E Licon; N Moreno; X Querol; N H Batis; J L Cortina

doi:10.1016/j.scitotenv.2018.02.243

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

Sci Total Environ. 2018 Jul 15:630:781-789. doi: 10.1016/j.scitotenv.2018.02.243. Epub 2018 Feb 27.

Authors

M Hermassi¹, J Dosta², C Valderrama³, E Licon⁴, N Moreno⁵, X Querol⁵, N H Batis⁶, J L Cortina⁷

Affiliations

¹ Chemical Engineering Department, Barcelona TECH-UPC, Barcelona, Spain; Department of Biological and Chemical Engineering, National Institute of Applied Sciences and Technology (INSAT), University of Carthage, Tunisia; Barcelona Multiscale Science and Engineering Research Center, Barcelona, Spain.
² Department of Chemical Engineering and Analytical Chemistry, Universitat de Barcelona (UB), Spain.
³ Chemical Engineering Department, Barcelona TECH-UPC, Barcelona, Spain; Barcelona Multiscale Science and Engineering Research Center, Barcelona, Spain. Electronic address: cesar.alberto.cesar.alberto.valderrama@upc.edu.
⁴ Chemical Engineering Department, Barcelona TECH-UPC, Barcelona, Spain.
⁵ Institute of Environmental Assessment and Water Research IDAEA, Consejo Superior de Investigaciones Científicas, Barcelona, Spain.
⁶ Department of Biological and Chemical Engineering, National Institute of Applied Sciences and Technology (INSAT), University of Carthage, Tunisia.
⁷ Chemical Engineering Department, Barcelona TECH-UPC, Barcelona, Spain; Barcelona Multiscale Science and Engineering Research Center, Barcelona, Spain; Water Technology Center, CETaqua, Cornellà de Llobregat, Spain.

PMID: 29499536
DOI: 10.1016/j.scitotenv.2018.02.243

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 (Mg₃(PO₄)₂(s)) or struvite (MgNH₄PO₄(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 0.7-1gNH₄⁺/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 (MgHPO₄(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.

Keywords: K-zeolite; Magnesium oxide; Na-zoelite; Nutrients recovery; Reactive sorbent; Sewage sludge anaerobic digestates.