The future of sustainable affordable housing in Kenya.

On 11th October 2022 President Ruto inspected the Kings Serenity Affordable Housing Programme project in Ongata Rongai. The Kings Serenity housing project is part of the Boma Yangu initiative whose main agenda is to provide affordable housing to Kenyans. The project aims to provide 15,000 affordable housing units.

The Kings Serenity project is part of former President Uhuru Kenyatta’s affordable housing programme under the Big Four agenda.

As well as the project in Ongata Rongai the programme also aims to build housing units in Mukuru kwa Reuben as well as other areas in the country.


With so many housing units being constructed there will be a huge strain on the existing infrastructure, including wastewater sewage management and water provision. CESP Africa has provided a wastewater management system to aid that strain.

We are in the process of installing a complete wastewater treatment plant that will be complete and operational before 2023, before residents move into the housing units. The treatment plant will not only treat the wastewater produced in the project but will also recycle water that can be used for watering plants and cleaning the environs.

The system is an important part of keeping the overall housing project affordable as it reduces the need for provision of water by other water providers.

The future.

As the Kings Serenity project comes to a close, we hope to be future partners in the provision of affordable housing in Kenya. Not only recycling wastewater but also providing treated water for future housing projects.

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New home owners often forget about wastewater treatment. Here is how you could save yourself if you plan ahead.

Building your own home is a dream for many people. Moving away from paying rent and stresses of having a landlord can be liberating. As you build your own home there are many considerations you have to make.

From the location you intend to build on to your budget (We’ll talk about this a bit more later in this blog) to the size of your home etc. There are so many things to keep in mind it can get overwhelming. For people planning on building in areas that don’t have a sewer system how you plan on dealing with your wastewater is a consideration to add to that long list.

Often people throw it at the bottom of the list of priorities. Saying things like “We’ll install a septic tank later”

The thing about wastewater treatment is that it can be deceptively expensive and cumbersome to deal with if you don’t plan well. As you are building your home when it comes to wastewater treatment you have a few options; physical water treatment, biological water treatment, chemical treatment, and sludge treatment.

A septic tank uses physical means to clean the wastewater. Septic tanks have their own considerations that we cover here.

Construction site view of a new septic tank.

Today we will look at why one of our domestic wastewater treatment systems could be the answer to your wastewater problems. To read about how exactly the system works you can read here.

Advantages of our wastewater treatment system

  • Efficiency.

Overall, the system is effective in its treatment of wastewater and also produces high quality effluent. The effluent is basically clean water that can be used to water plants or clean driveways.

Because of the reflux step in the treatment process, the system produces a small amount of sludge. Reducing associated maintenance cost and labor.

  • It’s a simple system to install and maintain.

The system comes as a complete and compact package that is ready to install. The only preparations required are digging a hole to fit the system and installing plumbing to get to the system. Maintenance is also simple as it only requires Biotreat, which is a wastewater treatment system additive, and OSS, which is the activated microbial culture.

Installation of our domestic wastewater treatment system.
  • It is a cost-effective system.

Installation is cheaper as it does not require any specialized equipment. Some other systems require structures that have to be specially made.

Maintenance is also cost effective.

Additional considerations

The system produces clean effluent, but it is not fit for human consumption unless additional treatment is done to it. Reverse osmosis filtration is suitable to completely clean the effluent, to read about it click here.

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How our wastewater system gives you clean water.

Wastewater treatment aims to get rid of the contaminants in wastewater to produce clean effluent. There are different treatment technologies to achieve this end, here we will go through the activated sludge treatment process. The process uses bacteria that biologically digests the solid matter in the wastewater to leave clean effluent as a final product. 

Flowchart of the activated sludge wastewater treatment process.

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Wastewater treatment process.

Flow regulation.

The flow equalization chamber receives the raw wastewater. A screen filters the raw wastewater going into the first chamber, large solid matter as well as material that can not be broken down by the system is filtered out. Undigestable material may include fabric, pads, surgical masks etc. Often issues in the wastewater treatment plant arise because of undigestable solid matter clogging up different stages in the treatment process (e.g. clogging pumps in the system) hence the screening process is very important.

The content and rate of flow into the system varies throughout the day hence this chamber aims to homogenize the wastewater as it goes into the system.

Anaerobic digestion.

The digestion process starts in this chamber. Bacteria breaks down the wastewater without using oxygen hence an anaerobic process. At this stage the bacteria breaks down the nitrogenous components of the wastewater.

Aerobic digestion.

In this stage, the effluent shall be treated in extended aerobic biological reactor. The system is designed for extended aeration mode where excess oxygen is provided for oxidizing the carbonaceous as well as the nitrogenous BOD present in the effluent.

The organic wastewater is introduced into a reactor where an aerobic bacterial culture is maintained in suspension. The reactor contents are referred to as the Mixed Liquor Suspended Solids (MLSS). In the reactor, the bacterial culture carries out the conversion in general accordance with the stoichiometry as under:


COHNS +O2 + NUTRIENTS –bacteria- CO2+NH3+ C5H7NO2+ other end products (Organic matter)

The aerobic environment in the reactor is achieved by the use of Mechanical Surface Aerators, which also serves to maintain the reactor contents in a completely mixed regime. After a specified period of time the mixture of new cells and old cells is passed into a secondary clarifier, where the cells are separated from the treated wastewater.

A portion of the settled cells is recycled back to the aeration tank to maintain the desired concentration of organisms in the reactor, and a portion is wasted. In this system due to the extended retention period in the reactor the bacteria enters into the endogenous respiration phase resulting in relatively simple end products and energy, stable end products are also formed. The endogenous respiration phase is represented by following equation:


C5H7NO2 + 5 O2 —————-CO2 + 2H2O + NH3 + energy

The effluent will then flow into the sedimentation tank.


 The effluent moves to the next chamber where it settles. Any remaining solid material settles to the bottom of the chamber. Clean water from the top of the chamber is flows into the next chamber.

Any solids that settle in this chamber are refluxed back to the anaerobic chamber where the solid matter is taken through the digestion process again. The material that settles at this stage also contains bacteria which can be reused to avoid need for constant repopulation of the bacterial in the system.

Middle water tank.

For systems that have additional filtration of the effluent, the middle water tank acts as temporary storage before filtration.

Sand filtration.

A sand filter removes any remaining suspended solids from the effluent.

Clean water tank.

The clean water tank stores clean effluent ready for use.

The effluent can be disinfected by adding chlorine.. Depending on local regulation the effluent may be drained away or used for irrigation, gardening etc.

Commercial wastewater treatment plant
A mid-sized activated sludge wastewater treatment system.

The activated sludge treatment process is a relatively simple, it is generally cheaper and easier to maintain. It can also be scaled up, from domestic systems to larger commercial systems.

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Blackwater and greywater, what’s the difference?

Water is possibly the most important resource to man. It is integral to so many of our activities. After use, the water is contaminated and not readily usable in many cases. The wastewater produced from different processes is not contaminated to the same extent. Hence the different classifications of wastewater. Blackwater and greywater.

What is greywater?

Greywater, also called sullage, is wastewater from households or office buildings from streams without fecal contamination. All streams except for the wastewater from toilets. Sources of grey water include sinks, showers, baths, washing machines or dishwashers.

A kitchen sink is a source of greywater.

What is blackwater?

 Blackwater is wastewater that contains feces, urine, water and toilet paper from flush toilets. The pathogens present in blackwater also distinguish it from greywater.

Blackwater being drained into a water body.

Why the distinction.

Though both may be wastewater the level of contamination is different, requiring different treatment.

Greywater is less contaminated than blackwater meaning treatment is simpler. Provided the greywater does not contain harmful chemicals such as soap and detergents it can be recycled for irrigation and other domestic uses. Organic matter from kitchens may provide an added bonus to plant life if used for irrigation.

Blackwater is more contaminated, meaning it requires more thorough treatment before it is fit for any other use.

 Treatment processes such as extended aeration may be used to treat the blackwater to produce clean effluent. Chlorine may be added to the effluent to kill any pathogens present in the effluent.

The scale of the treatment plant based on the size of the facility it is servicing and the population. There are home sewage treatment plants (also domestic wastewater treatment plants) or commercial wastewater treatment systems.

A commercial sized wastewater treatment plant designed and installed by CESP Africa.

These systems treat both black and greywater together giving clean effluent that can be used for irrigation and general cleaning. The effluent produced is also fit for dumping in the local drainage after certification by National Environmental Management Authority (NEMA)


Blackwater and greywater should be stored and treated separately, where possible, to be more energy efficient. Households and offices that actively reuse greywater have the added benefit of reduced cost associated with water while also being environmentally conscious.

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What you need to know about septic tanks.

What is a septic tank?

A septic tank is a tank typically placed underground, in which Settling and anaerobic processes reduce wastewater (solids and organics). Typically, septic tanks are made of concrete or are ready to install plastic tanks. Though their treatment efficiency is only moderate.

Septic tank systems are a type of simple onsite sewage facility.

Mistakenly, the term may be used to refer to a wastewater storage tank or a biodigester. These two are different and serve different purposes. A wastewater storage tank doesn’t treat the wastewater but only acts as a temporary hold before it is transported away. A bio-digester takes advantage of aerobic processes to more effectively break down the wastewater to give clean effluent.

Septic systems are also called:

  • onsite wastewater treatment systems,
  • decentralized wastewater treatment systems,
  • cluster systems,
  • on-lot systems,
  • individual sewage disposal systems, and
  • private sewage systems.

How it works.

Septic tanks usually comprise of one or two Large chambers depending on the needs of the people it serves.

A schematic of a septic tank.

The first chamber receives the wastewater and regulates its flow. The solid waste, being heavier, sinks to the bottom of the chamber. The liquid portion of the wastewater fills the first chamber until it reaches the inlet into the second chamber. The same happens in the second chamber until it fills the chamber. At the liquid then leaves the septic tank through an out let into a soak pit.

The fats and oils float on top of the liquid portion of the wastewater to form a layer of scum. The solid waste settles at the bottom of the septic tank’s chambers forming a sludge.

There are bacteria in the wastewater that anaerobically digest a portion of the waste. The rate of digestion is slow hence the sludge needs to be periodically emptied.

The soak pit is a covered, porous-walled chamber that allows water to slowly soak into the ground.

Considerations when choosing a septic tank

Size the system will occupy.

The size of the system is dependent on the number of people expected to use the system. Typically, the breakdown of wastewater in the septic tank is slow so it has to be dug deeper, than say a biodigester. Some may even be up to 7 meters deep.

Emptying the system.

The breakdown process is slow because the system only utilizes anaerobic processed, hence sludge usually accumulates in the tank.

Periodically the system will have to be emptied out using an exhauster or vacuum truck.

The soak pit.

The soil has to be able to soak up the liquid portion of the wastewater after the septic tank or stand the chance of saturating the nearby soil. This could form puddles of wastewater on the surface or in extreme cases collapse of the soak pit.

Why use a septic tank?

It might be your only option.

Many areas within Kenya, especially rural areas, do not have access to government provided wastewater treatment facilities. When faced with such a situation getting a septic tank to partially treat and hold waste water might be the only real option you have.

Public and environmental health.

Some more impoverished parts of the country that lack proper wastewater management systems resort to dumping their sewage, which is a huge public health and environmental risk. As a solution, one could use a septic tank to hold their wastewater.

What are my options?

When the local administration hasn’t provided a wastewater disposal solution your main options are a septic tank or an aerobic wastewater treatment system. The latter having its own advantages and considerations over a septic tank.

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How the cooking oil you pour down your drain is messing up your drainage.

Practically every meal you prepare at home will use cooling oil, grease or cooking fat. For such a coming ingredient it’s a mystery how we aren’t more prepared and knowledgeable as to how to get rid of it once we’re done cooking.

Don’t pour fats, oil or grease down the drain.

Cooking fat and grease might go down the drain as liquids but as soon as they cool down, they turn to solids. As other food particles go down the drainage system they get trapped. They accumulate to the point where it restricts flow down the drain or even complete blockage of pipes.

Cooking oil floats on water forming a film that traps solids moving down the drain, causing the same effect.

Clogged drainage pipe

A common solution is to pour hot water down the drain, but this is only a temporary solution. It also only moves the issue down the drainage system. Further down the system the oils and fats cool and solidify causing problems for the local wastewater treatment systems or your own system.

Pouring dish soap is the same story. It only temporarily breaks down oils and fats. Further down the drain it collects bringing the same problems.

How to get rid of your used cooking oil.

First of all, make sure the oil from your sufurias, pans etc. does not go down the drain as they are in the sink. Let the oil cool after cooking and wipe down your dishes before washing them.

A strainer can help prevent oil and food particles from going down the drain.

Oils, fats and grease should be placed in a non-recyclable container, e.g. a milk carton, then thrown out with the trash.

If it is in small amounts, once the oil cools, it can be thrown in the trash without placing in a separate container.

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Two Rivers Mall

Two Rivers Mall, the largest shopping mall in east and central Africa. Located between the Northern Bypass and Limuru Road and sits on a whopping 1.7 million square feet/39 acres, thus providing over 700,000 square feet of leasable space.

Two Rivers Mall is owned by Two Rivers Lifestyle Company Ltd which is a coalition of several firms including, Centum Group, the majority shareholder; Aviation Industry Corporation of China (Avic) and ICDC a state-owned firm.

The mall consists of medium density residential homes, office blocks, a shopping center, as well as a vast range of restaurants one of which is the City Lodge’s three-star 170 key hotel. Some other renowned tenants include Carrefour, the French retailer, which operates more than 12,000 outlets globally, and is the mall’s anchor tenant; the Turkish luxury fashion line LC Waikiki, Woolworths, Hugo Boss and Nike.

Right from the start of construction and overall development of the mall, the owners knew that they wanted the project to be compliant with international green standards. With this in mind, CESP Africa was subcontracted by Athena Properties Ltd –the property managers- to provide a wholesome and eco-friendly Wastewater Treatment solution.

CESP proposed a Moving Bed Biofilm Reactor (MBBR) Aerobic Wastewater Treatment System. These terms may seem complex and daunting, however what the system basically does is treat the collected waste water using bacteria, whose purpose is to feed on this waste. These bacteria are provided with oxygen in order for survival as well as to operate at optimal levels, thus the system is referred to as an aerobic wastewater treatment system. The MBBR technology employs polyethylene biofilm carriers which provide a protected and increased surface area to support the growth of these bacteria. It is this high-density population of bacteria that achieves high-rate biodegradation within the system, while also offering process reliability and ease of operation. At the end of this whole treatment process Two Rivers mall was to obtain colorless, odorless and environmentally-friendly effluent.

This was to be a one-of-a-kind system for CESP Africa as it would be one of the largest Wastewater Treatment Projects installed in Africa. CESP took up the challenge and with their long-time business partners JET Inc. embarked on the installation of what was to be a gargantuan system. Jet Inc. is an American firm and is the respected world leader in wastewater treatment technology. Since 1955, the firm has provided products that have been developed with the industry’s longest service life and lowest repair rates and CESP Africa is the authorized distributor of the Jet Inc. products in Sub-Saharan Africa.

CESP conducted multiple site visits, attended a good number of meetings with the different shareholders and fellow sub-contractors as well as designed and redesigned the layout and structure of the system together with the dedicated engineers at JET Inc. with painstaking attention to detail so as to ensure that not a single item was left out.

Installation of the 1,135 m3 / 300,000 GPD (Gallons per Day) or 1,135,624 liters per day Wastewater Treatment System then began with the CESP workmen and engineers working tirelessly to ensure the timely completion of the project. Besides, the wastewater treatment system, CESP also installed a Supervisory Control and Data Acquisition (SCADA) system. This SCADA system allows for remote monitoring, data logging as well as diagnosis of the installed wastewater treatment system hence providing CESP a timely, safer and overall, more efficient project maintenance procedure.

The mall has since been opened with a ribbon cutting ceremony that was held on the 14th of February 2017 and was graced by the Kenyan President Hon. Uhuru Kenyatta. It is approximated that 120,105 people visited the mall that day and CESP is proud to say that their Wastewater Treatment System was able to handle all the waste generated on that peak day and effectively continues to do so a couple of months down the line.

The Two Rivers Management puts this effluent (treated wastewater) to good use such as irrigating their expansive grounds as well as a reserve in the case of fire-fighting and any excess effluent is discharged into River Gichiie. All of this released effluent is in line with the requirements by the local environment regulator (NEMA) for discharge and reuse.

Through this partnership with CESP Africa, Two Rivers development is able to reuse 80% of all the water now and in the future creating a cyclic environment for the entire ecosystem. Additionally, it has created a sustainable shopping, living & working experience for all at the Two Rivers.

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