In this study simultaneous and continuous inline dosing of PAC and coagulant in UF was investigated. Surface water was directly treated with PAC-UF and performance of the system was assessed by looking at membrane fouling and organic micropollutants removal. Combining adsorption and membrane processes in one technique, hybrid membrane processes, enhances performance of OMP removal by membrane processes. Powdered activated carbon (PAC) combined with coagulation and ultrafiltration (UF) is a possible treatment technique for surface water.
Permeability in UF-membranes remains steady, when dosing coagulant. Only a small increase in irreversible fouling of 0.2-0.7*109 m-1h-1 is visible. However, absence of coagulant dosing causes irreversible fouling to increase to 8.7*1010 m-1h-1 and can not be easily reversed with a chemically enhanced backwash (CEB). Inline dosing of PAC alone causes an irreversible fouling of 11.4*1010 m-1h-1 and highest increase in reversible fouling of 11.7*1010 m-1h-1. Addition of coagulant (1.2 mg/l) lowers reversible fouling compared to no dosing, on the other hand addition of PAC to coagulant shows no clear increase or decrease in reversible fouling. Coagulation has a negative effect on capillary blocking, an increase of 4-8% compared to no coagulant or adsorbent. PAC and no dosing did not influence pore blocking.
Highest removal of low to good adsorbable OMP was 10-63% for continuous and simultaneous dosing of 12 mg PAC/l and 1.2 mg FeCl3/l. Increasing filtration time (30 to 60 min) showed highest removal efficiency of 75% of Sotalol and 5-Methyl-1H-Benzotriazole, both good adsorbable OMP. Removal of PFAS varies between a few percent and 37%. Continuous dosing of coagulant (1.2 mg/l) with PAC (10 mg/l) has a negative impact on OMP adsorption including PFAS. With a higher PAC dose (15 mg/l) removal efficiency was not affected.
Addition of coagulant with PAC-UF showed to be effective to prevent irreversible fouling, with direct surface water treatment. However, coagulation is responsible for blocking of capillaries even resulting in a small decrease of permeability. Removal of OMP including PFAS was much lower compared to other PAC-UF systems and therefore PAC-UF with simultaneous and continuous inline dosing of PAC is not a good set-up. Adjustments in set-up should be made in order to make this configuration work. Possible improvements are increase of filtration time between backwash and dosing sequence of PAC and coagulant.

The new concept of sewer mining which utilizes the ceramic nanofiltration (C-NF) membranes offers a compact solution for water and other resources recovery. However, since it has very limited pre-treatment process, membrane fouling is a common problem due to the direct contact between the membrane and sewage water. Sewage water contains a lot of extracellular polymeric substances (EPS) that can block the membrane pores. One of the most persistent EPS is sodium alginate which responsible for the gel layer formation on the membrane surface.

Removal of the alginate gel layer can be done by implementing chemical cleaning. However, too frequent chemical cleaning can damage the membrane and environmentally dangerous. Therefore, to make this new concept of sewer mining more feasible, the correct cleaning method to remove the fouling layer need to be found. From this point, the research objective for this research is formulated as “Investigation of fouling control methods that can prolong the time before chemical cleaning needs to be performed to achieve higher water production.”

Several methods such as forward flush, iron coating and calcium carbonate coating were investigated. Alginate filtration was done under constant pressure experiment and the effectivity of each cleaning method was calculated by measuring the change in water permeability after the cleaning. The results show that the iron and calcium carbonate coating followed by 5 min forward flush are able to achieve a permeability recovery of 40 to 90 %. Iron coating required 400 mg/l of iron hydroxide to be dossed and a minimum of 5 min reaction times with hydrogen peroxide to have a high permeability recovery. On the other hand, only 1 minute is required by 200 mg/l calcium carbonate dosing concentration with citric acid as a cleaning solution to achieve a similar improvement as the iron hydroxide coating. Both of the processes produce higher water productivity in 2 h of experiment than the chemical cleaning with 0.1 % sodium hypochlorite.

In the end, a theoretical projection on the real sewage water filtration was made to study the economic and environmental impact of the coating process. The results show the cost of production per m3 of clean water is 0.22 euro for iron hydroxide and only 0.12 euro for calcium carbonate. Furthermore, environmental impact assessment using Chain Management by Life Cycle Analysis (CMLCA) software which produced by Leiden University with Eco-indicator 99 (EI-99) categorization shows that calcium carbonate has less environmental burden than iron hydroxide coating.