Recovery Of Humic Substance From Leachate MBR+NF Concentrate By Nanofiltration And Two-stage Ultrafiltration Hybrid Process

Leachate MBR+NF concentrate with high concentration refractory organics is the bottleneck of the treatment of leachate.Given the high content of humic Substances(HS)in the concentrate,an novel concept for the recovery of HS as water-soluble fertilizer was proposed,and the reduction for the concentrate volume was achieved as well.A mixture of leachate MBR+NF concentrate generating from landfill and incineration leachate were used for the feed,and nanofiltration(NF)and two-stage ultrafiltration(UF)hybrid process was employed to recover HS from the concentrate.A serial experiments were conducted to investigate the separation performance of the integrated system on pilot sacle.In NF process,the flux increased with the increase of operational pressure,and the separation efficency between organics and salts also enhanced.However,temperature and pH had negligible effect on the flux and the retention of organics.During the concentration and desalting process,the flux declined linearly with increasing concentration factor(CF),while organics steadily increased with the organic rejection around 99.5%.However,the salt permeation decreased slightly,and separation factor(SF)escalated as a whole.In first stage UF process,the flux increased with the increase of operational pressure,and the retention of organics increased slightly,but the salt permeation decreased.As a whole,SF increased,meaning the effectively separating organics from salts.Also,the temperature and pH posed little influence on the flux and the rejection of organics.The heavy metals were enriched,yet the contents were rather low.During the concentration and desalting process,the flux decreased with the increase of CF,but the rejection of organics increased.The recovery of HS declined,and the salt permeation decreased slightly.SF was linearly correlated with CF,demonstrating that first stage UF could effectively separate and refine HS in the concentrate.The divalent ions of Ca2+,Mg2+ and SO42-were enriched significantly,except chloride ion with a negative rejection.In second stage UF process,characteristization of the influences of operational pressure,temperature and pH on separation performance was similar with those in first stage UF process.It is noteworthy that the increase in flux and organic rejection with CF in second stage UF process were higher than that in first stage UF process.However,variation of the recovery of HS and enrichment factor with CF for two stage UF process were the same.The enrichments of Ca2+,Mg2+and SO42-were slower and negative rejection for chloride ion was greater,comparing to those in first stage UF process.Besides,the recovery of HS and the salt permeation steadily decreased down to 86%and 45%respectively.A strong correlation still existed between the SF and CF data,which implied that the second stage UF process could further separate effectively the organics from the salts.The enrichments of heavy metals went on,hwoever,thecontents were still low.The end concentrate achieved with the two-stage UF process can meet the requirements of Chinese nation professional standards for water-soluble fertilizers containing HS.The heavy metal contents complied with the relevant standards as well.The permeate from NF process can meet the requirements of Chinese nation professional discharget sandards,which achieved the reduction of MBR+NF concentrate.In two-stage UF process,circulating the permeate from second stage UF process into the feed of first stage UF process could enhance the recovery of HS.In order to improve separation efficiency between organics and salts,and reduce the content of salts,the end concentrate achieved with the two-stage UF process was diluted by tap water and reconcentrated.