Combining submerged membrane technology with anaerobic and ...

Chapter 44.1. IntroductionThe application of anaerobic processes for treating low-strength wastewaters hasreceived high attention in recent years. One of the reasons is that it may guarantee theprocess sustainability with regard to the use of the aerobic processes due to the lowerenergy consumption, generation of a biogas with a high methane content and diminution ofbiomass production. Among all these technologies, the upflow anaerobic sludge blanket(UASB) reactor has been the most relevant due to its simplicity and compactness.UASB reactors have been proposed and applied to the treatment of various industrialwastewaters and even domestic wastewater in warm or tropical regions of the planetwhere the residual water has a temperature greater than 20 °C throughout the year(Seghezzo et al., 1998; Leitao et al., 2006). Its use has become popular in countries likeIndia, Pakistan, China, Colombia, Brazil, Indonesia and Egypt. On the contrary, the use ofUASB reactor for the treatment of urban wastewater in countries with cold or temperateclimates is not feasible due to a combination of interrelated factors such as low cellularproductivity and activity of microorganisms at these temperatures. Biomass losses in thefinal effluent might of UASB reactor may be compensated by the increased activity of thesludge at higher temperature (hot countries), but in countries with temperate or coldwastewater it results into a vicious circle in which the loss of biomass avoids to increasecapacity and the diminution of capacity prevents to produce the biomass that is required tocompensate the losses observed.Over the last decade, the adaptation of membranes coupled with anaerobicbiological processes has made anaerobic membrane bioreactors (AnMBR) a promisingalternative to conventional wastewater treatment. Moreover, the use of filtrationmembranes allows avoiding the observed biomass losses, and could make wastewatertreatment feasible even at lower temperatures (Judd, 2011). However, the main drawbackof using AnMBR is related with membrane fouling and the maximum operating flux thatcan be achieved. Feasible flux has a strong influence on both the capital and operationcosts of the process. Most of the authors working with AnMBR reported fluxes in the rangeof 5-15 L·m -2·h -1 at temperatures above 30 °C (Zhang et al., 2005; Saddoud et al., 2007;Trzcinski and Stuckey, 2009). Jeison and van Lier (2006) obtained critical flux values in therange 16-23 L·m -2·h -1 under mesophilic (30 °C), and 5-21 L·m -2·h -1 under thermophilic (55°C) conditions. In the case of domestic wastewater treated at ambient temperatures,operating fluxes are significantly lower. Robles et al. (2013) reported fluxes between 9 and13 L·m -2·h -1 treating municipal wastewaters at temperatures between 15 and 33 ºC. Lew et110