We supplied an 800 GPD (3,600LPD) reverse osmosis filtration system to a home in Nairobi county. The client was struggling with borehole water that discolored and had a large amount of suspended solids.
The client took a water sample thereafter had it analyzed and got the following results.
Borehole water analysis
| PARAMETER | Values | KS EAS 12:2018* | WHO standards | Remarks |
| Colour (Pt. Co. APHA Colour) | 561 | 50 | 15 | Fail |
| Turbidity (NTU TUB) | 83.1 | 25 | 5.0 | Fail |
| Total Suspended Solids (mg/L TSS) | 52 | ND | NIL | Fail |
| Iron (mg/L Fe) | 6.45 | 0.3 | 0.3 | Fail |
| Manganese (mg/L Mn) | 0.317 | 0.1 | – | Fail |
| Ammonia (mg/L NH3) | 1.7 | 0.5 | 0.5 | Fail |
| BACTERIOLOGICAL ANALYSIS | ||||
| Total Coliforms (cfu/100 ml TC) | 37 | ND | ND | Fail |
*The KS EAS 13:2018 specifies requirements for packaged mineral water for human consumption. This standard applies to natural mineral water, mineral water, natural spring water, spring water and carbonated mineral water.
The analysis confirmed our suspicions on what might be the main issues with the water. The dissolved iron and manganese were responsible for the colour of the water.
The findings led the design team to chose a reverse osmosis system, as it would remove all dissolved salts as well as any bacteria present in the water. A plant of 800GPD was chosen to match the needs of the household.
The plant also includes :
- Multi-grade sand filter,
- Greensand and DMI65
- Activated carbon filters.
How the plant works.
Water from the borehole is pumped into a 5,000-liter raw water tank. A pump directs the water through the first vessel with a multi-grade sand filter to remove any suspended solids. The second vessel contains Greensand and DMI65 which remove iron and manganese in the water. The third vessel contains activated carbon to remove chlorine* in the water.
*The chlorine kills any bacteria and viruses present in the water.
The water is then passed through a PP, Granular activated carbon and CTO filter to further filter out any suspended solids, colour, odors and bad taste from the water.
Another pump then passes the water through the reverse osmosis (R.O) filter to remove any dissolved salts from the water. Finally, tan ultraviolet filter kills any remaining pathogens in the water.
A 5,000 liter tank stores the now filtered water, ready for use.
Maintenance
The system is set to periodically backwash the 3 larger vessels, this prevents the filters from getting clogged with suspended solids and other contaminants in the water.
The R.O. filter is periodically backwashed to prevent it from clogging. The system is also set to automatically dose anti-scallant to prevent any buildup on the R.O. membrane.
The PP, Granular activated carbon and CTO filters are replaced as needed.
