Experimental study of ammonia removal from water by modified direct contact membrane distillation

In this work, a modified direct contact membrane distillation (MDCMD) with receiving solution in permeate was developed for accelerating ammonia removal from aqueous solution. The ammonia removal efficiency by means of DCMD, hollow fiber membrane contactor (HFMC) and MDCMD was comparatively investigated. And the effect of feed pH, temperature, flow rate and concentration on ammonia removal efficiency and the permeate flux in MDCMD process was studied. Experimental results showed that the ammonia removal efficiency of DCMD, HMC and MDCMD was 52%, 88% and 99.5% within 105min, respectively. In MDCMD, feed pH value was proved to be the most dominant factor and the optimal feed pH was 12.20. Increasing feed temperature and flow rate led to higher ammonia mass transfer coefficient, ammonia removal efficiency and permeate flux within the range studied. The initial ammonia concentration had a negligible effect on ammonia removal efficiency. Variation of feed ammonia concentration in HFMC, DCMD and MDCMD (HFMC: uf=0.5m/s, up=0.1m/s, feed pH=12.2; DCMD: Tf=50°C, Tp=28°C, uf=0.5m/s, up=0.1m/s, feed pH=12.2; MDCMD: Tf=50°C, Tp=28°C, uf=0.5m/s, up=0.1m/s, feed pH=12.2.). [Display omitted] •MDCMD with receiving solution in permeate was developed for ammonia removal.•Ammonia removal efficiency of DCMD, HFMC and MDCMD was investigated.•The feed concentration, pH, temperature and flow rate was studied.•The highest ammonia removal efficiency was observed in MDCMD.•Feed pH was the most dominant factor in MDCMD.