The schematic diagram below illustrates the water treat system tanks connection in a Domestic black and grey waste water treatment system which Express Drainage Solutions Kenya Ltd can design, supply and install;

The picture below illustrates such a domestic black and grey water waste water system tanks with all the above chambers which Express Drainage Solutions Kenya Ltd can supply and install for aerobic waste water treatment process


The aerobic waste water treatment process consists of several stages which are outlined below;

These processes are the following;

In Express Drainage Solutions Kenya Ltd set up of waste water treatment and recycling, black water and grey water do not mix in the bio-digester because grey water contains soap and detergent molecules which would otherwise kill the anaerobic bacteria needed for bio-digestion but the two types of water both mix in the aeration (Aerobic) chambers as indicated in the diagram above.
These processes which occur in each of the stages are the following;
i. Bio-digester
Treatment of the black water commences in a purpose designed unit known as the Bio-digester as indicated in the flow diagram above. This is the initial point of the wastewater recycling; at this point inlet is directly connected to the sewer drainage system. This is the chamber where the initial biological process (Anaerobic digestion) takes place due to the presence of anaerobic bacteria leading to formation of methane gas. This chamber is airtight to enable the survival of these anaerobic bacteria. At this stage there are various gas
processes as follow; Methane average 60%, Carbon dioxide 35% and other gases less than 5 %. However these gases are of no economic value at this stage because they are not contained in an expansion chamber to create pressure which would enable them to be used. The process takes 2 hours.
ii. Aeration chambers
From the Biodigester, the water flows to the aeration chambers, where air is pumped into large aeration tanks by the air blower. These chambers mix the wastewater and sludge that stimulates the growth of  oxygen using bacteria and other tiny organisms that are naturally present in the sewage. These beneficial micro-organisms consume most of the remaining organic materials that are polluting the water and this produces heavier particles that will settle later in the treatment process. At this stage, grey water which has already undergone filtration (Refer to diagrams above) to remove soap and detergent molecules and fiber is mixed with the bio-digested waste water for aeration purposes. Wastewater passes through these bubbling tanks in three to six hours.
iii. Clarification chambers
From the aeration chambers, the aerated wastewater then flows to the clarification tanks. Here the heavy particles and other solids settle to the bottom as secondary sludge. Some of this sludge is re-circulated back to the aeration tanks as “seed” to stimulate the activated sludge process. The re-turned sludge contains millions of micro-organisms that help maintain the right mix of bacteria and air in the tank and contribute to the removal of as many pollutants as possible. Clarification is the second last of the four steps in the process. Clarifiers consist of tanks which hold water or wastewater for a period sufficient to allow the sediments and other suspended materials to settle to the bottom. The clarification process makes the water clear by removing all kinds of particles, sediments, oil, natural organic matter and color. At this stage the wastewater is about 90-95 % pure.
iv. Chlorination chambers
The chlorination stage is where chlorinating agents are added to ensure 100% purity of the water. A chlorine dispenser ensures calibrated measures of chlorine are added to the water, while the submersible pump ensures that the water is pumped back to the storage tanks for reuse in the estates, households or institutions or alternatively pumped for irrigation. Disinfection with chlorine is necessary for safe potable water supplies and for healthy rivers and streams. Microorganisms are present in large numbers in sewage treatment plant effluents and waterborne disease outbreaks have been associated with sewage-contaminated water supplies or recreational waters.
Chlorination is by far the most common method of wastewater disinfection and is used worldwide for the disinfection of pathogens before discharge into receiving storage tanks, irrigation schemes, streams, rivers or oceans. Chlorine is known to be effective in destroying a variety of bacteria, viruses and protozoa, including Salmonella, Shigella and Vibrio cholera.
The types of filters for grey water which we can use for this process;
1) Coarse gravel and charcoal filter which is easy to make; this filter uses physical properties of stone, gravel, sand and charcoal to remove impurities from the water which include soap and detergent molecules as well as fibers and algae, a micro-organism green plant which is found in sewage water
2) Other various filter types also do exist

Benefits of recycled wastewater

Recycling our water can offer substantial benefits to our society including:

  • Reduction of nutrient and contaminant loads into oceans and rivers
  • Providing more drinking quality water for domestic uses by substituting drinking quality water with recycled water for irrigation of agricultural crops and amenity horticulture
  • Reducing demand and stress on freshwater resources such as the groundwater and rivers by providing alternative water supplies

There may also be benefits to agricultural and amenity enterprises through:

  • Guaranteed water supply
  • Supply of water quality underpinned with a comprehensive water quality assurance program Security for investment in agricultural enterprises
  • Recycling of valuable nutrients

There are also economic benefits like;
(a) Agriculture benefits such as: (i) reduced diversion costs, (ii) value of a secure “droughtproof”
Supply of reclaimed water, (iii) increased farm production, and (iv) value of reclaimed water nutrients = savings in fertilizer applications;
(b) Urban water supply benefits such as: (i) savings in the capital cost of diversion structures, drought storage, transfer systems and water treatment and (ii) savings in operation and maintenance costs including pumping energy and treatment chemicals;
(c) Urban wastewater benefits such as: (i) savings in discharge pump stations and pipelines and (ii) savings in treatment and nutrient removal costs required for discharge to sensitive waters

What are the advantages of the Black and Grey water treatment system?
  • Power Free Treatment;
  • Minimal Maintenance
  • Quiet Bio-System
  • Environmental Care
  • Versatile
  • Robust & Rugged
  • Good for Standard Toilet Systems
  • Great for Difficult Sites
  • Saves Your Water
  • Performance Guarantee
Who are the Target Beneficiaries?
  • Residential homes
  • Commercial buildings; Golf clubs, Hotels and Restaurants
  • Boarding schools
  • Institutions of higher learning
  • Health care facilities

Garden Chambers, 2nd Flr. Off Jeevangee Gardens, Mokhtar daddah Street

+254 727 160738

+254 738 627632

P.O.BOX 8620-00200, Nairobi, Kenya