A two-step crushed lava rock filter unit for grey water treatment at household level in an urban slum

A. Y. Katukiza*, M. Ronteltap, C. B. Niwagaba, F. Kansiime, P. N.L. Lens

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

36 Citations (Scopus)


Decentralised grey water treatment in urban slums using low-cost and robust technologies offers opportunities to minimise public health risks and to reduce environmental pollution caused by the highly polluted grey water i.e. with a COD and N concentration of 3000-6000mgL-1 and 30-40mgL-1, respectively. However, there has been very limited action research to reduce the pollution load from uncontrolled grey water discharge by households in urban slums. This study was therefore carried out to investigate the potential of a two-step filtration process to reduce the grey water pollution load in an urban slum using a crushed lava rock filter, to determine the main filter design and operation parameters and the effect of intermittent flow on the grey water effluent quality. A two-step crushed lava rock filter unit was designed and implemented for use by a household in the Bwaise III slum in Kampala city (Uganda). It was monitored at a varying hydraulic loading rate (HLR) of 0.5-1.1md-1 as well as at a constant HLR of 0.39md-1. The removal efficiencies of COD, TP and TKN were, respectively, 85.9%, 58% and 65.5% under a varying HLR and 90.5%, 59.5% and 69%, when operating at a constant HLR regime. In addition, the log removal of Escherichia coli, Salmonella spp. and total coliforms was, respectively, 3.8, 3.2 and 3.9 under the varying HLR and 3.9, 3.5 and 3.9 at a constant HLR. The results show that the use of a two-step filtration process as well as a lower constant HLR increased the pollutant removal efficiencies. Further research is needed to investigate the feasibility of adding a tertiary treatment step to increase the nutrients and microorganisms removal from grey water.

Original languageEnglish
Pages (from-to)258-267
Number of pages10
JournalJournal of Environmental Management
Publication statusPublished - 15 Jan 2014
Externally publishedYes


  • Grey water
  • Hydraulic loading rate (HLR)
  • Lava rock filter
  • Slums
  • Treatment


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