Treatment of polluted river water with a photocatalytic slurry reactor using low-pressure mercury lamps coupled with a membrane

A novel configuration of a photocatalytic slurry reactor using low-pressure mercury lamps coupled with membrane filtration was proposed, and treatment of polluted river water with a pilot plant of this system was investigated. Both + COD and NH4 -N in the river water were simultaneously removed. Under the conditions of a hydraulic retention + + time of 3.0 h, influent COD strength of 50–80 mg L!1 and NH4 -N of 2–6 mg L!1, 80% COD and 50% NH4 -N were achieved, respectively. The reactor was found to own a higher UV utilization effectiveness than most reported photocatalytic reactors. Intermittent backwash was effective to retard the membrane fouling and enable stable membrane operation for more than 1 month. An adhered catalyst, algae and fungi in the river water were the main contaminants of the membrane, but the membrane permeability could be almost recovered through sequential rinsing by tap water and a sodium hypochlorite solution. After continuous operation for over 1 month, the photocatalytic activity of catalysts was found elevated, which likely resulted from adsorption of hydroxyl-rich alcohols onto the catalyst surfaces.

A novel configuration of a photocatalytic slurry reactor coupled with membrane filtration was proposed. By a pilot treatment of polluted river water, the following conclusions were drawn: 1. The photocatalytic slurry reactor using lowpressure mercury lamps coupled with membrane filtration was capable of steadily treating polluted river water, removing 80% COD and 50% ammonia simultaneously under an HRT of 3 h.Based on experiments, UV energy utilization effectiveness was calculated to be 17 µg-COD J!1 and 7.0 µg-COD J!1 under batch and continuous conditions, respectively, higher than most reported experimental results. Besides, this reactor was capable of saving more land than those reported in the literature. 2. In continuous operation, intermittent backwash was effective to retard the membrane fouling. 3. The main foulants on the membrane surface were TiO2 powder, algae and fungi present in the influent. Sequential rinsing using tap water and sodium hypochlorite could almost recover the permeability of the membrane. 4. Catalyst activity after continuous treatment of river water was improved, and adsorption of hydroxyl-rich alcohols onto the catalyst surface seemed to contribute to this effect. The photocatalytic slurry reactor coupled with membrane filtration and UV radiation can be used to treat polluted river water. However, a complete economic analysis based on engineering design, including light source, UV lamps or solar radiation—or a combination of the two—is necessary to determine whether the method is economically viable or not.