6. Grey Water Management

Grey Water Management Scheme

Overview

Grey water is defined as “wastewater that is produced from household processes (e.g. washing dishes, laundry and bathing)” (Carden et al, 2007). There is a high volume of grey water produced in informal settlements with the expected average nearing 70 liters per day per household. Grey water can contain harmful bacteria and even faecal matter that contaminates soil and ground water. When coupled with the relatively high water table of many settlements, flooding in the winter rainy season often occurs, spreading this contaminated water. In order to address these issues our team explored methods of managing the flow and improving the quality of grey water with the hope that future testing will allow the reuse of grey water. This is especially important considering that the City of Cape Town is expected to face a water shortage by 2012 (Cape Times, 2009). The designs for grey water purification include an initial collection tank that then runs into two biofilters for purification. Wetland plants will be grown in the biofilters to absorb some water and also be used as a carbon source for composting. After purification, the water is channeled to soakaways.

System Components

• Initial Collection Tank
  • Collect grey water for initial testing
• Reed Bed Gravel Biofilter(s)
  • Partially purify and evaporate introduced grey water
  • Grow carbon media for composting
• Valved Piping on Each End of Biofilter
  • Employ natural evaporation as method of water removal in sunny conditions
• Soakaways
  • Dispel remaining water

Design Considerations and Specifications

• Target usage: 200 users
• Expected Daily Volume: 3500 litres
• Dimensions and Design Specifications pending Further Research

Operational Plan

• Source: Grey water from on-site taps, hand washing station, and laundry station.
• Maintenance: Replant gardens and clean gravel annually.
• Valve Control: Valves will be used to control the flow of grey water. On sunny days the valve can be closed to fill the biofilter with water for evaporation. On rainy or cloudy days the valve can be open and spill water to soakaways.

Experimental Research Recommendations

• Testing:
  • Define ideal method of grey water purification for informal settlement setting
    • Examine quality and composition of pre-treatment grey water
    • Experiment with different forms of grey water purification techniques and compare to effectiveness of initial biofilter
  • Qualify the feasibility of using grey water treated with a biofilter for agricultural use
    • Examine the effect of post-biofilter treated grey water on different plants to determine the possibility of using grey water for irrigation
    • Evaluate pathogen content in plants
• Data Collected:
  • Grey Water Quality, Pre- and Post-biofilter
  • Grey Water Volume

Background Research and Discussion

Biological methods for treating grey water are quite experimental, and a systematic way of determining the most effective methods has yet to be created. Therefore, in order to prevent our system from contaminating the surrounding soil, we have designed a dual flow tank that will simultaneously help us monitor the volume and quality of grey water collected. The figure below details the basic principle of a biofilter like that used in our Sanitation Centre designs. The grey water is collected in a traditional septic tank or a covered bark mulch pit and then directed into the gravel trickling filter by a perforated pipe. This gravel hosts natural microorganisms that break down harmful bacteria before recollecting in a secondary tank. This tank will allow easy access for testing purposes, and a failsafe collection point if the volume of water is higher than expected. The final step at this time will be a pipe directing the treated water to multiple planned soakaways. In the future, after extensive testing for pathogens and other contaminants, this pipe might direct the clean water back into the facility for controlled reuse.

1. Septic tank for grey water collection
2. Overflow pipe – perforated for water dispersal
3. Gravel bed trickling filter
4. Soil bed growing reeds or grass
5. Secondary collection tank for testing purposes
6. Soakaway pipe

– Toilets, Urinals, and Primary Waste Management – Composting & Pasteurization – Improved Taps – Hand Washing Station – Laundry Station – Grey Water Management Scheme– Caretaker Office – Facility Perimeter –