Pilot Scale Investigation on the Removal of Pollutants from Secondary Effluent to Meet Botswana Irrigation Standards Using Roughing and Slow Sand Filters
Botswana is an arid country that needs to start reusing wastewater as part of its water security plan. Pilot scale slow sand filtration in combination with roughing filter was investigated for the treatment of effluent from Botswana International University of Science and Technology to meet Botswana irrigation standards. The system was operated at hydraulic loading rates of 0.04 m/hr and 0.12 m/hr. The results show that the system was able to reduce turbidity from 262 Nephelometric Turbidity Units to a range between 18 and 0 Nephelometric Turbidity Units which was below 30 Nephelometric Turbidity Units threshold limit. The overall efficacy ranged between 61% and 100%. Suspended solids, Biochemical Oxygen Demand, and Chemical Oxygen Demand removal efficiency averaged 42.6%, 45.5%, and 77% respectively and all within irrigation standards. Other physio-chemical parameters were within irrigation standards except for bicarbonate ion which averaged 297.7±44 mg L-1 in the influent and 196.22±50 mg L-1 in the effluent which was above the limit of 92 mg L-1, therefore averaging a reduction of 34.1% by the system. Total coliforms, fecal coliforms, and Escherichia coli in the effluent were initially averaging 1.1 log counts, 0.5 log counts, and 1.3 log counts respectively compared to corresponding influent log counts of 3.4, 2.7 and 4.1, respectively. As time passed, it was observed that only roughing filter was able to reach reductions of 97.5%, 86% and 100% respectively for faecal coliforms, Escherichia coli, and total coliforms. These organism numbers were observed to have increased in slow sand filter effluent suggesting multiplication in the tank. Water quality index value of 22.79 for the physio-chemical parameters suggests that the effluent is of excellent quality and can be used for irrigation purposes. However, the water quality index value for the microbial parameters (1820) renders the quality unsuitable for irrigation. It is concluded that slow sand filtration in combination with roughing filter is a viable option for the treatment of secondary effluent for reuse purposes. However, further studies should be conducted especially for the removal of microbial parameters using the system.
 N. Hamoda, M F, Al-Ghusain, I, AL-Mutari, “Sand filtration of wastewater for tertiary treatment and water reuse,” vol. 164, pp. 203–211, 2004.
 E. M. Seeger, M. Braeckevelt, N. Reiche, J. A. Müller, and M. Kästner, “Removal of pathogen indicators from secondary effluent using slow sand filtration: Optimization approaches,” Ecol. Eng., vol. 95, pp. 635–644, 2016.
 V. K. Tyagi, A. A. Khan, A. A. Kazmi, I. Mehrotra, and A. K. Chopra, “Slow sand filtration of UASB reactor effluent: A promising post treatment technique,” Desalination, vol. 249, no. 2, pp. 571–576, 2009.
 G. Nakhla and S. Farooq, “Simultaneous nitrification-denitrification in slow sand filters,” J. Hazard. Mater., vol. 96, no. 2–3, pp. 291–303, 2003.
 P. D. Nemade, A. M. Kadam, and H. S. Shankar, “Wastewater renovation using constructed soil filter (CSF): A novel approach,” J. Hazard. Mater., vol. 170, no. 2–3, pp. 657–665, 2009.
 R. Li, Z. Zou, and Y. An, “Water quality assessment in Qu River based on fuzzy water pollution index method,” J. Environ. Sci. (China), vol. 50, pp. 87–92, 2016.
 S. Tyagi, B. Sharma, P. Singh, and R. Dobhal, “Water Quality Assessment in Terms of Water Quality Index,” Am. J. Water Resour., vol. 1, no. 3, pp. 34–38, 2013.
 M. G. Healy, M. Rodgers, and J. Mulqueen, “Treatment of dairy wastewater using constructed wetlands and intermittent sand filters,” Bioresour. Technol., vol. 98, no. 12, pp. 2268–2281, 2007.
 M. Achak, L. Mandi, and N. Ouazzani, “Removal of organic pollutants and nutrients from olive mill wastewater by a sand filter,” J. Environ. Manage., vol. 90, no. 8, pp. 2771–2779, 2009.
 K. Langenbach, P. Kuschk, H. Horn, and M. Kästner, “Slow sand filtration of secondary clarifier effluent for wastewater reuse,” Environ. Sci. Technol., vol. 43, no. 15, pp. 5896–5901, 2009.
 O. Nkwonta, “A comparison of horizontal roughing filters and vertical roughing filters in wastewater treatment using gravel as a filter media,” Int. J. Phys. Sci., vol. 5, no. 8, pp. 1240–1247, 2010.
 M. W. Jenkins, S. K. Tiwari, and J. Darby, “Bacterial, viral and turbidity removal by intermittent slow sand filtration for household use in developing countries: Experimental investigation and modeling,” Water Res., vol. 45, no. 18, pp. 6227–6239, 2011.
 J. K. Mwabi, B. B. Mamba, and M. N. B. Momba, “Removal of Escherichia coli and Faecal Coliforms from Surface Water and Groundwater by Household Water Treatment Devices/Systems: A Sustainable Solution for Improving Water Quality in Rural Communities of the Southern African Development Community Region,” Int. J. Environ. Res. Public Health, vol. 9, no. 12, pp. 139–170, 2012.
 S. Verma, A. Daverey, and A. Sharma, “Slow sand filtration for water and wastewater treatment – a review,” Environ. Technol. Rev., vol. 6, no. 1, pp. 47–58, 2017.
 P. Ncube, M. Pidou, T. Stephenson, B. Jefferson, and P. Jarvis, “The effect of high hydraulic loading rate on the removal ef fi ciency of a quadruple media fi lter for tertiary wastewater treatment,” Water Res., vol. 107, pp. 102–112, 2016.
 S. Chandra and A. Singh, “Evaluation of Physicochemical Characteristics of Various River Water in India,” vol. 8, no. 4, pp. 1546–1555, 2011.
 L. A. Valdez-aguilar, C. M. Grieve, J. Poss, and D. A. Layfield, “Salinity and Alkaline pH in Irrigation Water Affect Marigold Plants : II . Mineral Ion Relations,” vol. 44, no. 6, pp. 1726–1735, 2009.
 O. I. Nkwonta and G. M. Ochieng, “Total Dissolved Solids Removal in Wastewater Using Roughing Filters,” Chem. Sci. J., vol. 2010, no. CSJ-6, pp. 1–6, 2010.
 A. O. Ogunfowokan, J. F. Obisanya, and O. O. Ogunkoya, “Salinity and sodium hazards of three streams of different agricultural land use systems in Ile-Ife, Nigeria,” Appl. Water Sci., vol. 3, pp. 19–28, 2013.
 C. E. Maia and K. K. R. da P. Rodrigues, “Proposal for an index to classify irrigation water quality: a case study in northeastern Brazil,” Rev. Bras. Ciência do Solo, vol. 36, no. 3, pp. 823–830, 2012.
 D. M. Joshi, A. Kumar, and N. Agrawal, “Assessment of the irrigation water quality of river Ganga in Haridwar district,” Rasayan J. Chem., vol. 2, no. 2, pp. 285–292, 2009.
 A. Tal, “Rethinking the sustainability of Israel’s irrigation practices in the Drylands,” Water Research. 2016.
 V. A. Pacini, A. M. Ingallinella, and G. Sanguinetti, “Removal of iron and manganese using biological roughing up flow filtration technology,” Water Res., vol. 39, no. 18, pp. 4463–4475, 2005.
 W. Bellamy, “Slow Sand Filtration : Influences of Selected Process Variables,” no. September, 2014.
 T. K. Stevik, K. Aa, G. Ausland, and J. F. Hanssen, “Retention and removal of pathogenic bacteria in wastewater percolating through porous media: A review,” Water Res., vol. 38, no. 6, pp. 1355–1367, 2004.
 E. Guchi, “Review on Slow Sand Filtration in Removing Microbial Contamination and Particles from Drinking Water,” vol. 3, no. 2, pp. 47–55, 2015.
 A. B. Nancy, M. Josephine, and M. A. Lizzy, “Slow Sand Filtration of Secondary Sewage Effluent : Effect of Sand Bed Depth on Filter Performance,” vol. 3, no. 8, pp. 15090–15099, 2014.
 D. K. Boah, S. B. Twum, and K. B. Pelig-ba, “Mathematical Computation of Water Quality Index of Vea Dam in Upper East Region of Ghana,” Environ. Sci., vol. 3, no. 1, pp. 11–16, 2015.