The use of membranes for the treatment of manure: a critical literature review

Problems associated with surplus nutrients in areas with high livestock density could be partly solved by the use of membrane technology to concentrate manure nutrients in small volumes that could be exported as fertilisers to other agricultural regions. This article presents a critical review of the current state of research on the use of membrane filtration for manure concentration and treatment. Microfiltration and ultrafiltration membranes basically act as very efficient solid-liquid separators that can isolate nutrients associated with particles such as phosphorus. Ammonia and potassium retention requires nanofiltration or reverse osmosis. Manure pretreatment and ammonia concentration represent two major challenges to the use of reverse osmosis filtration for animal manure treatment. Pretreated manure concentration in 10-50% of the initial volume and transmembrane flux ranging from 2 to 65 l m-2h-1 have been reported with reverse osmosis systems. Permeate ammonia-nitrogen concentration ranged from 42 to 1508 mg l-1, depending on initial feed concentration and volume reduction. However, reported results are difficult to compare because of insufficient data on feed and concentrate characteristics, which have a major impact on permeate quality, ammonia volatilisation and flux. In addition, few controlled laboratory results are available, especially regarding long-term experiments on membrane fouling and cleaning requirements. Additional studies required for further technological development and economic analysis of the treatment are (1) the elaboration of data sets correlating system performance with manure characteristics and operating parameters; (2) the effect of various pretreatments on system performance; (3) the identification of the predominant fouling mechanisms and the elaboration of cleaning procedures; (4) a mass balance approach to quantify ammonia losses and elaborate strategies to minimise volatilisation; (5) the initiation of field studies to evaluate the fertiliser value of the concentrate and permeate reuse strategies. Crown Copyright © 2007.