Slow sand filtration of UASB reactor effluent: A promising post treatment technique Vinay Kumar Tyagi a , Abid Ali Khan a , A.A. Kazmi a , Indu Mehrotra a , A.K. Chopra b, ⁎ a Department of Civil Engineering, Indian Institute of Technology, Roorkee, India b Department of Zoology & Environmental Science, Gurukul Kangri University, Haridwar, India abstract article info Article history: Accepted 11 December 2008 Available online 6 October 2009 Keywords: BOD Coliforms Post treatment Slow sand filtration Suspended solids UASB The study was carried out to evaluate the feasibility of slow sand filtration as a promising post treatment method for the up-flow anaerobic sludge blanket (UASB) reactor effluent. Laboratory scale filter column of 10 cm diameter and 0.54 m sand media depth was used to study the process performance. It was found out that slow sand filtration with 0.43 mm effective sand size is the most effective at a filtration rate of 0.14 m/h. It is capable of removing 91.6% of turbidity, 89.1% of suspended solids (SS), 77% of chemical oxygen demand (COD) and 85% of bio-chemical oxygen demand (BOD), 99.95% of total and fecal coliforms (TC and FC) and 99.99% of fecal streptococci (FS). Slow sand filters efficiently reduce the mass of suspended material and extend the filter run for more time (7 days) at a hydraulic load of 0.14 m/h as compared to the hydraulic load of 0.19 m/h and 0.26 m/h. Therefore, due to excellent effluent quality, it can be said that slow sand filtration would be a promising technology for the post treatment of small-scale UASB reactor effluent in developing countries, where treated effluent can be reused for various recreational purposes i.e. gardening and irrigation, as well as for safe discharge. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The great increase in water demand due to the continuous growth of human population has aroused a strong interest in wastewater reuse as a way of industrial and municipal water supply. When appropriately treated and recycled, wastewater can become a feasible option as a water source. Furthermore, this alternative reduces the environmental impact [1]. A major dilemma in this context is regarding the choice of an appropriate treatment technology to achieve optimal reuse of water and nutrients at a minimal energy expense. Anaerobic treatment doesn't require oxygen and therefore no energy input is required and in turn will yield energy in the form of biogas (Methane: CH 4 ). Anaerobic treatment plants have limited space requirements and therefore can be planned at locations within or just outside the city [2]. In addition, due to low sludge production and better stability of the sludge under anaerobic treatment, the cost involved in further treatment of sludge can be considerably reduced [3]. However, the residual concentration of organic (BOD and COD) and microbiological (quantified by fecal coliforms) pollutants in the anaerobic reactor effluent usually exceeds the maximum permissible level prescribed by the effluent discharge standards of most developing countries including India [4–6]. From this standpoint, post treatment of anaerobic effluent is necessary to reduce these parameters to the required level. At present, UASB facilities in India are integrated with pond system for post treatment. However, due to low detention times, these integrated ponds are found to be ineffective for the removal of pathogens, BOD and TSS. Nevertheless, several studies show that pathogenic microorganisms and BOD 5 and TSS can be removed by various systems such as aerated lagoons, downflow hanging sponge (DHS), rotating biological contractor, trickling filters, biological aerated filters [1,2,7,8]. Most of these processes require high energy and a huge capital cost for operation and maintenance and in addition even the effluent quality is not in compliance with the standards for the disposal. Regarding the effluent quality, cost efficacy and operational simplicity, slow sand filtration can be considered as one of the most promising post treatment options. Various researchers investigated the effectiveness of slow sand filters for tertiary treatment of wastewater at laboratory and pilot scale using different hydraulic loading and sand size, and suggest that slow sand filters are capable of removing BOD and SS, turbidity and total coliforms up to 86%, 68%, 88% and over 99%, respectively [9–13]. Slow sand filters have been used for the treatment of high quality surface waters [14–16], as well as for the treatment of secondary effluents [9,17–22]. The sand filters have multiple variables and have been conventionally designed on hydraulic loadings as well as on organic loading rates. It is an economical technique which requires less skilled manpower due to its simplicity [23–27]. Although a lot of work has been carried out on slow sand filters as a tertiary treatment process of biologically treated municipal sewage, Desalination 249 (2009) 571–576 ⁎ Corresponding author. E-mail addresses: vinayiitr@rediffmail.com (V.K. Tyagi), abidkdce@iitr.ernet.in (A.A. Khan), kazmifce@iitr.ernet.in (A.A. Kazmi), indumfce@iitr.ernet.in (I. Mehrotra), profakchopra@yahoo.co.in (A.K. Chopra). 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2008.12.049 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal