A study on the PP hollow fiber membrane contactor and its performances for removing ammonia from wastewater or mixed gas: I. Removal and recovery of ammonia from wastewater

Abstract

Recent research indicated that hydrophobic microporous hollow fiber membrane Contactor could be used to separate volatile contaminants from wastewater efficiently. The factors that influence the effect of separation of NH3/H2O are investigated carefully. It is found that the average diameter of micropores, porosity and gas penetration rate of polypropylene (PP) hollow fiber membrane are maximized synchronously at draw elongation 260%. The modules assembled with this PP hollow fiber membrane have good performance for separation of NH3/H2O. It is found that the overall mass transfer coefficient (K) only is dependent on the temperature and flux of ammonia solution and independent of the pressure and concentration of ammonia solution. Concentration of absorbing acid influences slightly the overall transfer coefficients K while the absorbent supply is sufficient. Under this condition, the relationship between transfer coefficient and raw ammonia water flow rate can be described using the Sieder and Tate equation. K is directly proportional to v1/3 (v stands for the flow rate of ammonia solution). The removal rate of NH3 was about 96-98% in the lab. Further industrial tests have been carried out individually in catalyst and chemical fertilizer factories to treat wastewater containing ammonium, whose concentration ranged from 1000-10,000g/m3. Wastewater treatment amount was 9.6 m3/day and 24 m3/day in catalyst and chemical fertilizer factories respectively. Average removal rate of NH3 was 93.5% during 5 months of continuous operation in the catalyst factory. The fouling is not heavy because the wastewater containing ammonia did not pass through the membrane wall. It is efficient to get rid of membrane fouling by washing the membrane with dilute acid and the cleanout period was 3 days. PP hollow fiber membrane can be produced by the melt-spinning and drawing method. This paper also investigates the relationship between processing condition of PP hollow fiber membrane and its structure and performance.