初始pH值对正渗透浓缩城市污水和回收磷的影响

为实现从城市污水中回收磷和水资源并同时减少后续处理反应器容积的目的，采用正渗透膜对城市污水进行浓缩，并探究城市污水的初始pH值对浓缩效果和磷回收的影响.首先采用合成城市污水进行正渗透浓缩试验，当提高原料液（FS）的初始pH值至9.5时，FS体积浓缩接近初始体积的1/10后，膜上及垫网上吸附磷含量约为其初始总量的44%，有利于磷的回收.当采用实际城市污水作为FS时，在初始pH值为9.5条件下进行浓缩后，污染膜面存在松散团聚的圆球颗粒，使得该条件下膜面污染物更易被洗脱，膜清洗后水通量高于不调节pH值条件下的水通量.膜原位超声清洗后，浓缩污水变为悬浊液，经静置沉降后收集沉淀物，其主要成分为CaCO₃、鸟粪石和磷酸镁类物质.当初始pH值为9.5时浓缩所得沉淀物中的CaCO₃和鸟粪石含量更高.调节城市污水初始pH值至9.5左右，对其进行三轮42h的连续运行浓缩后，污水的体积浓缩倍数约为8倍，磷回收率可达到63.9%.浓缩结束后，对膜先后进行原位超声清洗和碱洗加酸洗的化学清洗，清洗后膜通量约为初始通量的78%.浓缩后污水的pH值在8.5~9.1之间，且COD/TN值明显提高（从3.6至11.5），有利于后续的生物脱氮除磷.

Effects of the initial pH on the process of forward osmosis for concentration of municipal sewage and phosphorus recovery

In order to recover phosphorus and water resources from municipal sewage and reduce the reactor volume for subsequent treatment, forward osmosis membrane was used to concentrate municipal sewage. The effect of different initial pH on municipal sewage concentration and phosphorus recovery was explored. When forward osmosis concentration test was carried out with synthetic sewage, as the initial pH of feed solution (FS) was raised to 9.5 and the volume of FS was concentrated to 1/10 of the initial, the adsorbed phosphorus on the membrane and the spacer was about 44% of the initial total, which was conductive to phosphorus recovery. When FS was real municipal sewage and the initial pH of it was 9.5, there were agglomerated spherical particles on the fouled membrane surface, making the membrane surface pollutants more easily cleaned under this condition, and the water flux of membrane after cleaning was higher than that under the unadjusted pH conditions. After in-situ ultrasonic cleaning, the concentrated sewage became a suspension solution. The main components of the collected precipitate were CaCO₃, struvite and magnesium phosphate. When initial pH was 9.5, the contents of CaCO₃ and struvite in the resulting precipitate was higher than that under the other operating conditions. After adjusting the initial pH of the municipal sewage to 9.5 and concentrating it for three consecutive runs of 42 hours, the volume of the sewage was concentrated to about 8 times of the original volume, and the phosphorus recovery reached 63.9%. After the concentration is completed, the membrane was firstly subjected to in-situ ultrasonic cleaning, and then to chemical cleaning with alkali washing and acid washing. After cleaning, the water flux was about 78% of the initial membrane flux; the pH of the concentrated sewage was between 8.5~9.1; the COD/TN value was significantly increased from 3.6 to 11.5, which was conducive to the subsequent nitrogen and phosphorus removal process.