Performance of Full-Scale Thermophilic Membrane Bioreactor and Assessment of the Effect of the Aqueous Residue on Mesophilic Biological Activity

Abstract

To date, the management of high-strength wastewater represents a serious problem. This work aims to evaluate the performance on chemical pollutants and on sludge production of one of the two full-scale thermophilic membrane bioreactors (ThMBRs) currently operational in Italy, based on monitoring data of the last two and a half years. Removal yields on COD, N-NOx, non-ionic and anionic surfactants (TAS and MBAS), increased with the input load up to 81.9%, 97.6%, 94.7%, and 98.4%, respectively. In the period of stability, a very low value of sludge production (0.052 kgVS kgCOD−1) was observed. Oxygen uptake rate (OUR) tests allowed us to exclude the possibility that mesophilic biomass generally exhibited any acute inhibition following contact with the aqueous residues (ARs), except for substrates that presented high concentrations of perfluoro alkyl substances (PFAS), cyanides and chlorides. In one case, nitrifying activity was partially inhibited by high chlorides and PFAS concentration, while in another the substrate determined a positive effect, stimulating the phenomenon of nitrification. Nitrogen uptake rate (NUR) tests highlighted the feasibility of reusing the organic carbon contained in the substrate as a source in denitrification, obtaining a value comparable with that obtained using the reference solution with methanol. Therefore, respirometric tests proved to be a valid tool to assess the acute effect of AR of ThMBR on the activity of mesophilic biomass in the case of recirculation.

Numerical Analysis of a Full-Scale Thermophilic Biological System and Investigation of Nitrate and Ammonia Fates

“…The biological tank have a diverse oxygen concentration. This management strategy allows both the aerobic removal of the organic substance in zones with oxygen concentration (2 mgO 2 L −1 ), and the denitrification in anoxic zones (<1 mgO 2 L −1 ) [13,14]. As previously mentioned, the TBR is coupled with an ultrafiltration system due to the poor sedimentation of the thermophilic sludge.…”

“…For instance, in previous works, a thermophilic biological process was combined with an ultrafiltration membrane system to overcome sludge settleability issues and maximize performance, guaranteeing purification yields of the organic load of 95% [11]. This technology also granted the ability to treat different types of pollutants in high-strength AW in terms of COD content and surfactants [12] being applied in two full-scale plants [13,14].…”

How to Produce an Alternative Carbon Source for Denitrification by Treating and Drastically Reducing Biological Sewage Sludge

“…Ammonia in permeate was stripped before tests to avoid possible inhibition of microorganism. The method described also in our previous study was used [25]. Total of 500 mL of biomass was aerated for 30 min and mixed with 500 mL of substrate, enriched with nitrates using KNO 3 to obtain an initial N-NO x concentration in the starting sample of approximately 50 mg/L.…”

“…The second full scale removed 78.2% of COD (operating with an organic loading rate (OLR) between 1.5 and 2 kg/(m 3 d), and almost 82% of COD in case of an OLR greater than 3 kg/(m 3 d). In this case, a specific sludge production of 0.052 kg VSproduced /kg CODremoved was highlighted [25].…”

“…Regardless of the substrate being fed, ThAlMBR produces a carbonaceous aqueous residue (permeate). In recent work, the feasibility of reuse permeate, from ThAlMBR fed with aqueous waste, in denitrification processes as alternative carbon source was proved [25]. If the amount of organic substance in the untreated WW is too low in relation to the required COD:N ratio, the addition of an external carbon source becomes necessary to increase the yields of the denitrification process [26,27].…”