Nitrogen removal from wastewater by an immobilized consortium of microalgae–bacteria in hybrid hydrogels

Abstract

The high content of nitrogen in wastewater brings some operational, technical, and economical issues in conventional technologies. The aim of this study was to evaluate the nitrogen removal by hybrid hydrogels containing consortium microalgae–nitrifying bacteria in the presence of activated carbon (AC) used as an adsorbent of inhibitory substances. Hybrid hydrogels were synthesized from polyvinyl alcohol (PVA), sodium alginate (SA), biomass (microalgae–nitrifying bacteria), and AC. The hybrid hydrogels were evaluated based on the change in ammonium (NH4), nitrate (NO3), and chemical demand of oxygen (COD) concentrations, nitrification rate, and other parameters during 72 h. Results indicated that NH4 removal was more effective for hydrogels without AC than with AC, without significant differences regarding consortium biomass concentration (5 or 16%), presenting final concentrations of 3.13 and 3.75 mgNH4/L for hydrogels with 5 and 16% of the biomass, respectively. Regarding NO3 production, hydrogels without AC reached concentrations of 25.9 and 39.77 mgNO3/L for 5 and 16% of the biomass, respectively, while treatments with AC ended with 2.17 and 1.37 mgNO3/L. This confirms that hydrogels can carry out the nitrification process and do not need AC to remove potential inhibitors. The best performance was observed for the hydrogel with 5% of biomass without AC with a nitrification rate of 0.43 mg N/gTSS·h.

Influence of PFDA on the nutrient removal from wastewater by hydrogels containing microalgae-bacteria

“…In this relation, the microalgae are responsible for assimilating high loads of NH 4 –N and CO 2 to produce O 2 ; while the bacteria uptake the organic matter present in the medium and produces CO 2 and NO 3 . This symbiotic process of microalgae-bacteria for NH 4 –N assimilation has been reported to occur in SA beads [ 49 ], as well as in PVA + SA beads [ 50 ]. In the presence of PFDA, the removal of NH 4 –N can be attributed to AC due to low nitrate production.…”

“…The three types of hydrogels namely, HB, HC, and HBC, were synthetized in our experiment. All hydrogels were synthesized following the procedure previously reported [ 42 ], and just adding inoculum (consortium microalgae-bacteria), AC (size < 45 μm, HYCEL), or both. Briefly, hydrogels were produced from a solution polyvinyl alcohol (PVA, (C 4 H 6 O 2 ) n , Kuraray), sodium alginate (SA, (C 6 H 7 NaO 6 ) n , Sigma Aldrich) and a fraction of biomass in deionized water (DI).…”