Hybrid process of BAC and sMBR for treating polluted raw water

Presence of powdered activated carbon/zeolite layer on the performances of gravity-driven membrane (GDM) system for drinking water treatment: Ammonia removal and flux stabilization

Gravity-driven membrane (GDM) filtration is a promising alternative for decentralized water supply, while its widespread application was hindered by the poor removals of organics and ammonia during long-term operation. In this study, powered activated carbon (PAC) and granular zeolite were selected as typical adsorbents to investigate the impacts of pre-deposited adsorbent layers on contaminant removal and membrane fouling. Results showed that the pre-deposited PAC layers exhibited higher removal of organics than the control, while the zeolites deposited layers exhibited low removal of organics. The presence of PAC only enhanced the NH₄⁺ removal at subsequent stable stage, while zeolites were effective in deal with sudden high NH₄⁺ concentration due to ion exchange. The presence of mixed adsorbents layers had similar organic removal with PAC and NH₄⁺ removal with zeolite. The pre-deposited PAC layers could effectively alleviate membrane fouling in short-term UF tests, while the stable fluxes (5.88-6.54 L/(m²·h)) in long-term GDM operation were slightly lower than the control (6.63 L/(m²·h)). The zeolites deposited layer aggravated membrane fouling in both short-term ultrafiltration and long-term GDM (5.03-3.84 L/(m²·h)), but a higher stable flux (6.10 L/(m²·h)) was observed for GDM using the mixed adsorbents. The pre-deposited adsorbent layers resulted in increased concentrations of biomass, tri-phosphate (ATP) and extracellular polymeric substances (EPS), forming cake layers with a denser structure than the control. Finally, the fouling mechanism for GDM using different adsorbent layers was proposed based on fouling analysis and characteristics of biological fouling layer. The results and conclusion in this study could provide helpful information for the application of GDM with pre-deposited adsorbent layer in treating raw water with organics and/or sudden high ammonia concentration to produce potable water.

Algae-Laden Fouling Control by Gravity-Driven Membrane Ultrafiltration with Aluminum Sulfate-Chitosan: The Property of Floc and Cake Layer

Gravity-driven membrane (GDM) ultrafiltration is a promising water treatment method due to its low energy consumption and low maintenance. However, the low stable permeability in algae-laden water treatment is currently limiting its wider application. With the ultimate goal of increasing permeability, the aim of this study was to evaluate the effect of a composite coagulant of aluminum sulfate-chitosan (AS-CS) on the GDM filtration performance. In parallel tests with a single AS coagulant and without pre-coagulation, the analysis of membrane fouling resistance and the membrane fouling mechanism were evaluated. The results indicated that the AS-CS/GDM system can alleviate 23.74% and 58.80% membrane fouling, respectively, compared with AS/GDM and the GDM system. The AS-CS/GDM system can effectively remove humic-like substances having a molecular weight (MW) of 3–100 kDa, resulting in removal of 98.32% of algae cells and removal of 66.25% of dissolved organic carbon; the AS-CS/GDM system thereby improved the concentration of attached biomass on the membrane surface with the stronger biodegradability of organic matters. The application of AS-CS pre-coagulation in the GDM process could enhance the proliferation of microorganisms and the removal of low molecular weight humic-like substances. Therefore, the AS-CS/GDM system is a potentially important approach for algae-laden water treatment.

Effect of PAC dosage in a pilot-scale PAC-MBR treating micro-polluted surface water

To address the water scarcity issue and advance the traditional drinking water treatment technique, a powdered activated carbon-amended membrane bioreactor (PAC-MBR) is proposed for micro-polluted surface water treatment. A pilot-scale study was carried out by initially dosing different amounts of PAC into the MBR. Comparative results showed that 2g/L performed the best among 0, 1, 2 and 3g/L PAC-MBR regarding organic matter and ammonia removal as well as membrane flux sustainability. 1g/L PAC-MBR exhibited a marginal improvement in pollutant removal compared to the non-PAC system. The accumulation of organic matter in the bulk mixture of 3g/L PAC-MBR led to poorer organic removal and severer membrane fouling. Molecular weight distribution of the bulk liquid in 2g/L PAC-MBR revealed the synergistic effects of PAC adsorption/biodegradation and membrane rejection on organic matter removal. Additionally, a lower amount of soluble extracellular polymer substances in the bulk can be secured in 21 days operation.

Removal of anaerobic soluble microbial products in a biological activated carbon reactor

The soluble microbial products (SMP) in the biological treatment effluent are generally of great amount and are poorly biodegradable. Focusing on the biodegradation of anaerobic SMP, the biological activated carbon (BAC) was introduced into the anaerobic system. The experiments were conducted in two identical lab-scale up-flow anaerobic sludge blanket (UASB) reactors. The high strength organics were degraded in the first UASB reactor (UASB1) and the second UASB (UASB2, i.e., BAC) functioned as a polishing step to remove SMP produced in UASB1. The results showed that 90% of the SMP could be removed before granular activated carbon was saturated. After the saturation, the SMP removal decreased to 60% on the average. Analysis of granular activated carbon adsorption revealed that the main role of SMP removal in BAC reactor was biodegradation. A strain of SMP-degrading bacteria, which was found highly similar to Klebsiella sp., was isolated, enriched and inoculated back to the BAC reactor. When the influent chemical oxygen demand (COD) was 10,000 mg/L and the organic loading rate achieved 10 kg COD/(m3 x day), the effluent from the BAC reactor could meet the discharge standard without further treatment. Anaerobic BAC reactor inoculated with the isolated Klebsiella was proved to be an effective, cheap and easy technical treatment approach for the removal of SMP in the treatment of easily-degradable wastewater with COD lower than 10,000 mg/L.

Microbial community characterization, activity analysis and purifying efficiency in a biofilter process

The growth and metabolism of microbial communities on biologically activated carbon (BAC) play a crucial role in the purification of drinking water. To gain insight into the growth and metabolic characteristics of microbial communities and the efficiency of drinking water treatment in a BAC filter, we analyzed the heterotrophic plate count (HPC), phospholipid, dehydrogenase, metabolic function and water quality parameters during start-up and steady-state periods. In the start-up process of the filter with natural biofilm colonization, the variation in heterotrophic plate count levels was S-curved. The total phospholipid level was very low during the first 5 days and reached a maximum value after 40 days in the filter. The activity of dehydrogenase gradually increased during the first 30 days and then reached a plateau. The functional diversity of the microbial community in the filter increased, and then reached a relatively stable level by day 40. After an initial decrease, which was followed by an increase, the removal rate of NH4(+)-N and COD(Mn) became stable and was 80% and 28%, respectively, by day 40. The consumption rate of dissolved oxygen reached a steady level after 29 days, and remained at 18%. At the steady operation state, the levels of HPC, phospholipid, dehydrogenase activity and carbon source utilization had no significant differences after 6 months compared to levels measured on day 40. The filter was shown to be effective in removing NH4(+)-N, NO2(-)-N, COD(Mn), UV254, biodegradable dissolved organic carbon and trace organic pollutants from the influent. Our results suggest that understanding changes in the growth and metabolism of microorganisms in BAC filter could help to improve the efficiency of biological treatment of drinking water.

Measuring the activity of heterotrophic microorganism in membrane bioreactor for drinking water treatment

In order to quantify the activity of heterotrophic microorganism in membrane bioreactor (MBR) for drinking water treatment, biomass respiration potential (BRP) test and 2,3,5-triphenyl tetrazolium chloride-dehydrogenase activity (TTC-DHA) test were introduced and modified. A sludge concentration ratio of 5:1, incubation time of 2h, an incubation temperature that was close to the real operational temperature, and using a mixture of main AOC components as the substrate were adopted as the optimum parameters for determination of DHA in drinking water MBR. A remarkable consistency among BDOC removal, BRP and DHA for assessing biological performance in different MBRs was achieved. Moreover, a significant correlation between the BRP and DHA results of different MBRs was obtained. However, the TTC-DHA test was expected to be inaccurate for quantifying the biomass activity in membrane adsorption bioreactor (MABR), while the BRP test turned out to be still feasible in that case.