BZN Wastewater Treatment Plant: Remove the Smell and the Exhauster Bill

A full septic tank that needs regular exhauster visits, and the bad smell that comes with it, is solved by the BZN Wastewater Treatment Plant, which digests wastewater on site through a four-chamber bio-septic tank and releases it safely into a soak drain, provided your property has the land to support one.

The problem you already know too well

You know the drill. The tank fills up, you call an exhauster, you pay for a truck that disrupts your compound and leaves a smell behind, and a few months later you do it all again. If you are a homeowner or landlord, that is a recurring cost and a recurring inconvenience for tenants. If you manage a school, hostel, barracks, or other institution, it is also a compliance question, since wastewater from institutions is repeatedly flagged as a leading source of urban pollution in Kenya.

There’s a better way: digest it properly, then let the land finish the job

Instead of simply holding raw sewage until a truck arrives, the BZN Wastewater Treatment Plant breaks it down through proper anaerobic digestion before it ever leaves the tank. It is best understood as a more advanced version of a household biodigester septic tank: where a basic biodigester breaks waste down and holds it, the BZN Wastewater Treatment Plant carries that same digestion through four chambers and a proper drain field, so the final effluent is cleaner and odorless rather than simply reduced in volume.

Sewage flows from the washrooms through pretreatment and screening, into a four-compartment bio-septic digester, and then out to a soakage French drain wetland or horizontal constructed wetland, where the land does the final work of absorbing the treated water safely.

This is not a compact, drop-in unit. It is a properly engineered bio-septic and drain field system, sized to your population and built into your site according to the Kenya Ministry of Water and Irrigation’s practice manual for sewerage and sanitation services. That means it needs enough land for the drain field to work, which is the one condition worth understanding clearly before you commit.

How the BZN Wastewater Treatment Plant actually works

The system follows a defined, standards-based process:

1. Primary screening. Grit collection trenches and 2mm spaced stainless steel grilles remove large non-biodegradable solids such as plastics, tins, and grit before they can interfere with digestion, using non-corrosive treated steel, stainless steel, or plastic screening media.
2. Pre-treatment and mixing. Effluent is dosed with a waste-formulated anaerobic microbial culture and enzymes, such as Septozyme BFB, which reduce sludge volume, cut odour, speed up bacterial oxidation, and increase the effective capacity of the system.
3. First chamber: primary settlement. This chamber receives raw waste and traps inorganic and non-biodegradable material, including plastics, sanitary pads, and baby diapers, which are removed during routine maintenance. It also traps fat and grease and provides the first stage of settlement. Dosing this chamber with SeptoClean BFB helps digest trapped fats and lipids before they can interfere with the chambers that follow.
4. Second chamber: anaerobic digestion. This chamber is airtight and inoculated with bacteria and enzymes, creating the optimum environment for anaerobic digestion, where most organic solid waste is broken down into water and gas. Periodic dosing with Bamoyeast BFB keeps sludge that settles on the chamber floor properly digested, reducing how often it needs manual removal.
5. Third and fourth chambers: secondary settlement and clarification. These chambers allow maximum settlement of suspended solids and enable denitrification, which further reduces ammonia and makes the final effluent odorless.
6. Filtration. 0.5mm filtration bio-restrainers, fitted between the third and fourth chambers and at the outlet, ensure the final effluent is over 90% solids-free before discharge.
7. Soakage French drain wetland or horizontal constructed wetland. Clean water exits the fourth chamber to a drain field sized specifically to your site’s population, soil type, and water table, either soaking evenly into the ground or being drained for irrigation use. On sites where the drain field sits above the outlet level of the tank, a discharge pump moves the treated water forward; on most sites, gravity alone carries it through.

What this actually means for you

• No more exhauster trucks, for good. Continuous anaerobic digestion, combined with proper settlement and filtration, removes the need for periodic tank pump-outs entirely.
• Odor eliminated at the source. Denitrification in the third and fourth chambers reduces ammonia specifically so the final effluent is odorless, not just diluted.
• Sized to your actual population, not guesswork. Tank and drain field volumes are calculated from your expected number of users and daily flow per person, following the same design method used for a proposed 700-person site: a properly sized four-compartment tank and matching drain field, not an undersized generic unit.
• Water you can reuse for irrigation. Treated water exiting the drain field is nutrient-rich and suitable for irrigating plants and vegetables, adding value to a garden or landscaped compound rather than simply disappearing underground.
• Straightforward, low-tech reliability. With no membrane, aeration blowers, or electronic control panel required, this is a simpler, more mechanically forgiving system than a full MBR plant or even some biodigester setups, which can matter where technical maintenance support is harder to access.
• Built to a recognized national standard. Tank and drain field sizing follows the Kenya Ministry of Water and Irrigation’s 2008 practice manual for sewerage and sanitation, giving you a defensible, standards-based design rather than an improvised one.
• Safe distances designed in. The tank and soak drain are positioned at defined minimum distances, 7.5m and 30.0m respectively, from any stream or water source, protecting both your compliance position and the surrounding environment.

The one condition that matters most: land

This system’s effluent still depends on the ground to finish treatment. The soak drain or horizontal constructed wetland needs enough land, with adequate infiltration capacity, to absorb the volume your property produces. A site with heavy clay soil or very limited land may not be a fit for the BZN Wastewater Treatment Plant in its standard form, and that is worth confirming honestly during a site assessment rather than after installation. If your property has generous land, reasonably permeable soil, and enough distance from water sources, this system is a proven, standards-compliant, and lower-complexity way to eliminate exhauster dependence.

Who the BZN Wastewater Treatment Plant is built for

• Homeowners with enough land for a soak drain who want to eliminate exhauster costs without the complexity of a full membrane treatment plant.
• Landlords managing rental properties with adequate compound space, looking for a lower-maintenance system than a conventional septic tank or basic biodigester, without the smell and service disruption.
• Schools, hostels, barracks, and similar institutions with defined populations and enough land on site, where a properly sized bio-septic and drain field system can be engineered to national standards, as has been done for large-scale residential accommodation projects.
• Any property with soil that drains reasonably well, since the system’s final treatment step depends on the land’s infiltration capacity rather than a mechanical process.

Common questions, answered honestly

Do I still need land for a soak pit with this system? Yes. Unlike a membrane-based plant, the BZN Wastewater Treatment Plant relies on a soakage French drain wetland or horizontal constructed wetland to complete treatment, so adequate land and reasonably permeable soil are required.

Will this work on clay soil? Not reliably in its standard form. The drain field’s infiltration rate is calculated based on soil type, and heavy clay significantly limits how well the ground can absorb treated water. A site assessment will confirm whether your soil is suitable.

How is the tank sized? Tank and drain field volumes are calculated from your expected population, daily water use per person, and a retention time of 48 hours, following the Kenya Ministry of Water and Irrigation’s 2008 practice manual.

Is the treated water safe to use? Water from the drain field is nutrient-rich and good for irrigation, but it is not fit for domestic use or animal consumption, as it still contains contaminants that remain harmful to humans and animals even after treatment.

What kind of maintenance does it need? The first chamber requires periodic removal of trapped inorganic waste such as plastics and sanitary items during routine maintenance sessions; beyond that, the digestion process runs continuously without mechanical intervention.

How far does the tank and drain need to be from water sources? A minimum of 7.5m for the bio-septic tank and 30.0m for the soak drain from any stream or water source, protecting both compliance and environmental safety.

The real cost comparison

Every exhauster visit is a recurring cost that never stops for as long as you rely on a holding tank or a basic biodigester alone. A properly digested, filtered, and drain-field-discharged system removes that cycle entirely after a single, well-designed installation, and because the BZN Wastewater Treatment Plant does not require membranes, blowers, or a control panel, it is typically a lower-complexity and lower-cost investment than a full MBR plant, provided your land can support the drain field it needs.

Ready to find out if your land is right for this system?

The land your property has, and the soil it sits on, are the two things that determine whether the BZN Wastewater Treatment Plant is the right fit. The next step is a site assessment: our engineers will review your population, available land, soil type, and proximity to water sources, and confirm the right tank and drain field sizing for your property, with no obligation.

For more information, visit us at our office at the junction of Kahawa Sukari Avenue and Muranga Road in Kahawa Sukari, or contact us at +254 111 715 578 or info@biozone.co.ke.