Effect of flocculation pre-treatment on membrane nutrient recovery of digested chicken slurry: Mitigating suspended solids and retaining nutrients

Abstract

Use of membrane filtration is attracting increasing attention for nutrient recovery from anaerobically digested slurry. However, the challenge is to reduce membrane fouling by effective solids mitigation, while maintaining valuable nutrients. In this study, the effects of several flocculation pre-treatments using polyaluminium chloride, iron chloride, and flocculant aid at various dosages were investigated. The results showed significant improvement in membrane flux from 0.8 to 27.6 mL/m 2 /s due to solid 2 migration (up to 75% removal). Significant loss of PO4 3− -P (99%) and humic acids (40-80 %) was observed. However, the content of NH4 + -N and indoleacetic acids was largely maintained in the treated slurry. Moreover, toxic metals were significantly removed through flocculation, making the final product risk-free of heavy metals for agricultural application.

Chemically Enhanced Solid–Liquid Separation of Digestate: Suspended Solids Removal and Effects on Environmental Quality of Separated Fractions

“…As reported by the manufacturer, resulting dosages of PAC and PACDE (Table 2) were approximately one order of magnitude higher than the usual application rates in the field of sludge treatment. Also, the range of tested PAC dosages (i.e., 1.8-3.6 g/L) was almost half than that tested in a similar study involving digested chicken slurry (i.e., 6-24 g/L) [19]. On contrary, tested DEED and PAM dosages are similar to those used in the wastewater sector and, solely for the use of PAM on digestates, to what reported in the scientific literature [19,30].…”

“…Also, the range of tested PAC dosages (i.e., 1.8-3.6 g/L) was almost half than that tested in a similar study involving digested chicken slurry (i.e., 6-24 g/L) [19]. On contrary, tested DEED and PAM dosages are similar to those used in the wastewater sector and, solely for the use of PAM on digestates, to what reported in the scientific literature [19,30]. According to 2020 market pricing, the cost of the chemicals used for the 3 best-performing treatments would be around 6 €/m 3 and 40 €/m 3 of unseparated digestate, respectively for PAC4 and PACDE5-PACDE6.…”

“…2e). As suggested by Luo et al [19], P removal could have been related more with the absorption of orthophosphates by PAC than precipitation with the suspended particles. Furthermore, a lower dissolved P concentration was reported as a key factor in decreasing inorganic fouling of membranes caused by precipitation of orthophosphates salts [10,13].…”

“…Also, related publications studied different chemicals dosages according to experimental design not always reliably comparable. However, the use of PAC + CPAM at a maximum dosage of 24 + 0.2 g/L was reported to decrease up to 23% of TSS concentration of the separated liquid parts of swine digested slurries after 24 h of settling (i.e., no centrifugation) [19]. Similarly, several mixtures of aluminum-based coagulants (10 g/kg) with polyelectrolytes (2 g/kg) and bentonite (5 g/kg), spiked before centrifugation, mitigated the TSS down to a range of 33 -100 g/L in the liquid fraction of digestates from anaerobic co-digestion of sewage sludge, food waste and slaughterhouse waste [20].…”

“…In the wastewater treatment sector, Polyaluminum chloride (PAC), polyacrylamide (PAM) and epichlorohydrine-dimethylamine with Ethylendiamine (DEED) are among the most efficient coagulant and flocculant products used for sludge dewatering [17]. Some authors demonstrated the efficacy of PAC and cationic PAM, under very different dosage configurations, on digested residues from AD of pig slurries and other agro-industrial substrates [11,18,19]. Further, Borowski et al [20] assessed the effects of several CES products on digestates from a pilot-scale co-digestion of lab-reconstructed food waste, slaughterhouse waste and municipal sewage sludge.…”