The treatability of landfill leachate by direct contact membrane distillation and factors influencing the efficiency of the process

Abstract

a b s t r a c tLandfill leachate is a high-strength wastewater with high concentration of harmful pollutants and is produced in almost all countries with high variation in constituents. In this study, a modified direct contact membrane distillation (DCMD) has been used to investigate the treatability of raw and pretreated landfill leachate. Two different hydrophobic membranes, polytetrafluoroethylene (PTFE) and polyvinylidene difluoride membranes with two different pore sizes (0.22 and 0.45 µm, respectively) were used and performed at three various delta temperatures (∆T); 30°C, 40°C and 50°C. The rejection efficiencies for conductivity, COD, sulfate, alkalinity and hardness were approximately 85%, 99%, 95%, 90% and 98%, respectively, with raw leachate and 99%, 98%, 92%, 85% and 98%, respectively, with pretreated leachate, while NH 4 + -N removal efficiency was about 70% and 92% for raw and pretreated leachate, respectively. The highest transmembrane fluxes (TMF) were obtained at a ∆T of 50°C with 0.45 µm pore size of PTFE membrane. The highest TMF with raw leachate was 9.87 L/m 2 h while it was 15.54 L/m 2 h with pretreated leachate. Contact angles and Fourier transform infrared spectroscopy were used to evaluate the resistance of the membranes to wetting and fouling.

Fouling and wetting in the membrane distillation driven wastewater reclamation process – A review

“…This adsorption-desorption process ensues recurrently until the humic acid reaches and disperse into the permeate [142]. Ammonia (NH 4 -N) rejection in MD has been reported to be poor in different types of organic wastewater treatment and reclamation in comparison to other kinds of contaminants [143,144]. Low NH 4 -N rejection may be attributed to the preferential generation of volatile ammonia gas and its permeation through membrane pores during the heating process [144].…”

“…Ammonia (NH 4 -N) rejection in MD has been reported to be poor in different types of organic wastewater treatment and reclamation in comparison to other kinds of contaminants [143,144]. Low NH 4 -N rejection may be attributed to the preferential generation of volatile ammonia gas and its permeation through membrane pores during the heating process [144]. Recovery of water from raw and biologically pre-treated municipal wastewater by DCMD using PTFE and PVDF membranes was calculated to yield…”

“…Also, the increase in feed stream temperature resulted in a higher temperature gradient across the membrane, which favored volatilization of ammonia gas and its permeation through the membrane pores [143]. DCMD of raw landfill leachates using PTFE and PVDF membranes (operational conditions in Table 1) demonstrated high rejection efficiencies for most of the water quality parameters (conductivity, alkalinity, hardness, COD, sulfate) but a low rejection of NH 4 -N (Table 2) [144]. The presence of organic biomass in wastewater resulted in an observable decrease in vapor pressure (due to the non-volatile fraction of biomass) in feed water and reduced the permeate flux in DCMD system to more than 50% and 70% of initial flux value (2.09 L/m 2 /h) for 6 and 12 g/L biomass, respectively after 72 hours of operation [145].…”

“…surfaces reduced wettability and fouling while reclaiming pre-treated municipal wastewater [143] and landfill leachates [144], and also enabled flux recovery by water flushing in textile/dyeing wastewater recovery over a more extended operational period [124] average pore diameter 30 Å, and 1000 m 2 /g, respectively) [127]. Whereas, significantly faster loss of hydrophobicity with the PTFE membrane was observed when raw RO concentrate was used as feed water (mainly due to the combined adhesion of hydrophilic organics and inorganic CaCO 3 on the membrane), which did not improve through water or acid washing [127].…”

“…Therefore, of the two pre-treatment processes, the integrated microfiltration-DCMD method was found to be more useful for obtaining clean water from olive mill wastewater [157]. Application of membrane bio-reactor (anoxic, aerobic and ultrafiltration) as a pre-treatment for the landfill leachates demonstrated better effluent quality and higher flux in MD due to reduced organic contaminants in feed water [144].…”