Prolonging the Life Span of Membrane in Submerged MBR by the Application of Different Anti-Biofouling Techniques

The membrane bioreactor (MBR) is an efficient technology for the treatment of municipal and industrial wastewater for the last two decades. It is a single stage process with smaller footprints and a higher removal efficiency of organic compounds compared with the conventional activated sludge process. However, the major drawback of the MBR is membrane biofouling which decreases the life span of the membrane and automatically increases the operational cost. This review is exploring different anti-biofouling techniques of the state-of-the-art, i.e., quorum quenching (QQ) and model-based approaches. The former is a relatively recent strategy used to mitigate biofouling. It disrupts the cell-to-cell communication of bacteria responsible for biofouling in the sludge. For example, the two strains of bacteria Rhodococcus sp. BH4 and Pseudomonas putida are very effective in the disruption of quorum sensing (QS). Thus, they are recognized as useful QQ bacteria. Furthermore, the model-based anti-fouling strategies are also very promising in preventing biofouling at very early stages of initialization. Nevertheless, biofouling is an extremely complex phenomenon and the influence of various parameters whether physical or biological on its development is not completely understood. Advancing digital technologies, combined with novel Big Data analytics and optimization techniques offer great opportunities for creating intelligent systems that can effectively address the challenges of MBR biofouling.

[Nitritation Performance of Zeolite Moving Bed Biofilm Reactor for Ammonium Wastewater Treatment]

A new type of zeolite-suspended packing was developed by using zeolite as an important raw material, which was then used to start the zeolite moving bed biofilm reactor (ZMBBR). ZMBBR was compared with the ceramsite moving bed biofilm reactor (CMBBR) packed with ordinary ceramsite-suspended packing to investigate the different nitritation performance. The results showed that stable nitritation was successfully achieved in two reactors by the inhibitory effect of free ammonia (FA), and both of their nitrite accumulation rates (NAR) reached 90%; due to the adsorption of zeolite to ammonium, ZMBBR relieved the inhibition of FA on AOB faster than CMBBR and achieved nitritation earlier; CMBBR and ZMBBR could maintain long-term stable nitrosation when ρ(NH₄⁺-N) was 350 mg·L^-1 and 1050 mg·L^-1 and NPR_AVG was 0.43 kg·(m³·d)^-1 and 1.26 kg·(m³·d)^-1, respectively, and ARE_CMBBR=82.21% and ARE_ZMBBR=88.85%. In the process of the influent ρ(NH₄⁺-N) gradually increasing from 250 mg·L^-1 to 1250 mg·L^-1, the maximum nitrite production rate (NPR) of CMBBR was 0.5634 kg·(m³·d)^-1; when ρ(FA) reached 166 mg·L^-1 at the influent ρ(NH₄⁺-N) of 750 mg·L^-1, CMBBR broke down for the heavy inhibition of FA. The maximum NPR of ZMBBR was 1.800 kg·(m³·d)^-1, and the performance of ZMBBR was getting worse after the ρ(FNA) reached the peak value of 1.9611 mg·L^-1 at the influent ρ(NH₄⁺-N) of 1250 mg·L^-1. Subsequently, the ρ(FA) of ZMBBR reached 158 mg·L^-1 rapidly, the NPR dropped significantly to 0.9028 kg·(m³·d)^-1, and the performance of ZMBBR became significantly worse. It was demonstrated by high-throughput sequencing analysis that the dominant strain of ZMBBR and CMBBR was Nitrosomonas_europaea, and the relative abundances of N._europaea in ZMBBR and CMBBR were 11.15% and 10.92%, respectively.

[Start-up of CANON Process and Short-cut Nitrification in a Pilot-scale MBBR Reactor]

Using a 150 L moving bed biofilm reactor (MBBR), with the temperature controlled at 28℃ and high NH₄⁺-N concentration (average concentration 350 mg·L^-1), inorganic wastewater was used as an influent to start the completely autotrophic nitrogen removal over nitrite (CANON) process. Meanwhile, the flocculent sludge was taken into a 5 L sequencing batch reactor, and the influent NH₄⁺-N concentration was maintained at 90-200 mg·L^-1 for the recovery of short-cut nitrification. The results showed that in the MBBR reactor, when the average hydraulic retention time (HRT) was 12 h, short-cut nitrification and total nitrogen (TN) removal rate were mutually constrained, the average TN removal rate was 38.2%, and the average δNO₃^--N/TN value was 0.274; when the HRT dropped to 6 h, the δNO₃^--N/TN value decreased from 0.347 to 0.146. The sequencing batch reactor (SBR) maintained aeration and anoxic time for 30 min and 20 min, respectively, by intermittent aeration, while the dissolved oxygen concentration during the aerobic process was 0.5 mg·L^-1 to 0.6 mg·L^-1, the free nitrous acid concentration was higher than 0.18 mg·L^-1 at the end of each cycle, NAR increased from 0 to 99.2% after 12 days, NUR decreased to 0 from an initial 24.8 mg·(g·h)^-1, and the TN removal rate decreased from 13% to 3%; the system successfully converted to short-range nitrification. High-throughput sequencing results showed that the abundance of Candidatus Kuenenia in the flocculent sludge and biofilm in the MBBR reactor were 7.91% and 17.38% respectively, Nitrosomonas accounted for 27.43% and 2.55%, respectively, while Nitrospira accounted for 0.30% and 0.28%, respectively. After the recovery of short-cut nitrification in the SBR, the abundance of ammonia-oxidizing bacteria and anaerobic ammonia oxidation decreased to 1.18% and 0.01%, respectively, and the abundance of Nitrospira increased to 1.39%.

[Start-up and Performance Optimization of a CANON Pilot Reactor]

A completely autotrophic nitrogen removal over nitrite (CANON) reactor was established by seeding ordinary activated sludge with reject water as the influent at (30±3)℃ from a sewage treatment plant in Qingdao. To solve bacterial loss and optimize reactor performance, a suspension of biological carriers was added to the CANON reactor. The result showed that the reactor was successfully started 130 days later. The total nitrogen removal load was up to 0.03 kg·(m³·d)^-1, and the average variation ratio of nitrate and ammonia (R_NaA) was 0.09, which was close to theoretical value 0.11. The CANON active sludge reactor ran for 300 days. During the stable operation period, the total nitrogen removal rate was stable at 0.20 kg·(m³·d)^-1. Red granular sludge was mixed with the effluent of the system, and the particle size of granular sludge was between 1 and 3 mm. The suspension carriers were added to the CANON reactor with a filling rate of 30%. The fillers added to the moving bed biofilm reactor (MBBR) were mature fillers in the nitrifying reactor of the laboratory. The accumulation rate of nitrification was greater than 95%, and the ammonia-oxidized surface load reached 2.0 g·(m²·d)^-1. After 30 days of operation and culturing, the system was successfully converted to a pure membrane system, and the biofilm on the surface of the carrier turned pale red. The total nitrogen removal load was up to 0.17 kg·(m³·d)^-1. The average R_NaA was 0.14, which was slightly higher than the theoretical value of 0.11. This suggested that the CANON sludge adapted to the environment in the MBBR and began to enter a stable stage. The CANON-MBBR ran for 200 days. During the stable operation period, the total nitrogen removal rate was stable at 1.15 kg·(m³·d)^-1. The biofilm was bright brick red with a thickness of 150-250 μm. MLSS and MLVSS on the carriers were approximately 10200 mg·m^-2 and 9000 mg·m^-2, respectively, and the total biomass in the system was approximately 1.5 kg. Through high-throughput sequencing, AOB and AnAOB were found to be the dominant bacteria species on the suspension carrier, with a relative abundance of 26.24% and 30.08%, respectively, and nitrate oxidizing bacteria were successfully suppressed. The above results showed that CANON-MBBR with high-density polyethylene filler as the suspension carrier had good nitrogen-removal efficiency and was conducive to the stable operation of the autotrophic nitrogen removal process.

Carrier effects on tertiary nitrifying moving bed biofilm reactor: An examination of performance, biofilm and biologically produced solids

Increasingly stricter ammonia and nitrogen release regulations with respect to wastewater effluents are creating a need for tertiary treatment systems. The moving bed biofilm reactor (MBBR) is being considered as an upgrade option for an increasing number of wastewater treatment facilities due to its small footprint and ease of operation. Despite the MBBRs creation as a system to remove nitrogen, recent research on MBBR systems showing that the system's performance is directly related to carrier surface area and is irrespective of carrier shape and type has been performed exclusively on chemical oxygen demand (COD) removal systems. Furthermore, the influence of carrier type on the solids produced by MBBR systems has also been exclusively studied for COD removal systems. This work investigates the effects of three specific carrier types on ammonia removal rates, biofilm morphology, along with solids production and settleability of tertiary nitrifying MBBR systems. The study concludes that carrier type has no significant effect on tertiary nitrifying MBBR system performance under steady, moderate loading conditions. The research does however highlight the propensity of greater surface area to volume carriers to become clogged under high loading conditions and that the high surface area carriers investigated in this study required longer adjustment periods to changes in loading after becoming clogged.