Lodges, schools, hospitals and estates often sit beyond a municipal sewer, or on one that cannot take the load. They have to treat their own sewage, and once that water has been treated properly, they often ask the next question: can we reuse treated sewage water for irrigation instead of sending it away? This guide explains how a modular sewage treatment plant works stage by stage, where ozone disinfection fits, what reuse involves, and what to settle before you buy a plant.
Why sewage needs engineered treatment
Wastewater from commercial facilities is a mixture of organic waste, suspended solids, nutrients and microorganisms. Left untreated, it brings several problems at once:
- High organic load. Measured as BOD and COD, which show how much oxygen is needed to break down the organic matter in the water, biologically (BOD) and chemically (COD).
- Suspended solids and sludge. Solids that settle, accumulate and have to be removed.
- Odour. A day-to-day problem on a site where people live, work or study.
- Pathogenic microorganisms. These must be reduced before the water is discharged or reused.
- Nutrient loading. Nitrogen and other nutrients that affect what the water can be used for.
- Compliance. Discharge requirements and, where water is reused, requirements for the reuse itself.
No single process solves all of that. Treatment works by putting several stages in sequence, each one preparing the water for the next.
What "modular" means
A modular sewage treatment plant is built from standard treatment units rather than designed from scratch for every site. Biozone's systems can be deployed in several configurations:
- containerised treatment plants
- skid-mounted treatment systems
- modular treatment units
- integrated plant installations
The point of the modular approach is scale. Capacity can be matched to the wastewater flow and added to as the facility grows. Biozone specialises in commercial plants for facilities generating 5 kilolitres a day and above, such as lodges and resorts, estates and residential developments, schools and hospitals, shopping centres, industrial facilities and remote infrastructure.
The stages of sewage treatment
A typical commercial sewage treatment process runs through these stages.
Primary treatment
Screening or primary settling separates large solids and sediment from the incoming sewage before the biological stage.
Biological treatment
Biological treatment is the core of most sewage treatment systems. In aerated tanks, aerobic bacteria break down organic waste, converting pollutants into stable biomass and treated water, which reduces the organic load. This stage includes nitrification followed by denitrification, the two steps that deal with nitrogen. Nitrification converts ammonia to nitrate, and denitrification then converts nitrate to nitrogen gas, which leaves the water. That is how the biological stage reduces the nitrogen part of the nutrient loading before the water moves on.
Clarification
After the biological stage, the water passes into clarification tanks, where biological solids settle out and separate from the treated water. Sludge collected here is removed periodically for further treatment or disposal. Clarification matters for the next stage too: clearer water gives disinfection a better chance to work.
Ozone disinfection
Ozone disinfection is the final treatment stage in this sequence. Ozone is a strong oxidant. It is generated on site and dissolved into the clarified water to reduce microbial contaminants and odours, which can mean relying less on stored chemical disinfectants. Correctly engineered, ozone disinfection is designed to avoid leaving long-term chemical residuals in the treated water.
Ozone breaks down quickly, so how well it does its job depends on the water it meets. Water that is still cloudy or carries a lot of organic matter uses up more ozone, which is one reason the earlier stages matter. Because ozone reacts with whatever is in the water, by-products can form, so treated water should be tested rather than assumed to be right.
Reusing treated sewage water for irrigation
Treated wastewater can often be reused for non-potable purposes. Reuse applications include:
- Irrigation of landscaping and agriculture
- Cooling water for industrial processes
- Toilet flushing and facility cleaning
- Environmental restoration
Reuse can reduce reliance on fresh water, which matters most where the supply is limited. These are non-potable uses: treated sewage water is not drinking water.
Whether your treated water is suited to irrigation depends on three things: the quality the plant delivers, what you plan to irrigate and the requirements that apply to that use. Quality is tested, not assumed, and requirements differ between sites and crops. Check what applies to your operation, including for irrigation of anything that people eat or that animals graze, before you plan the reuse. Where water is reused on grounds or crops, think about how the treated water is stored and delivered to the irrigation system, too. Treated water can still carry fine solids, nutrients and salts, which can affect filters and emitters, so ask how the irrigation system will cope.
Farms and estates considering reuse can read more on Biozone's agriculture page.
Design starts with your wastewater
Every sewage treatment system begins with an evaluation of the wastewater and the way the facility operates. Biozone engineers design systems around:
- daily wastewater flow rates
- facility occupancy and usage patterns
- organic loading characteristics
- discharge or reuse requirements
- environmental compliance standards
A school with holiday breaks, a lodge with seasonal peaks and a hospital that runs all day and night produce very different flow patterns. A plant sized only for the average flow can struggle at the peaks and be oversized in the quiet periods. Matching the configuration to the real flow is the first design decision, and it is made before equipment is chosen.
A treatment plant also needs routine inspection and performance monitoring to keep running as designed. Ask any supplier what monitoring and technical support come with the plant.
Where wastewater fits in Biozone's wider work
Sewage treatment is one part of Biozone's wastewater treatment capability. Where a site has specialised industrial wastewater that needs advanced treatment processes, Biozone works with trusted engineering partners.
Talk to an engineer before you buy a plant
Biozone has been in business for 25 years. We are a South African engineering company that designs on-site treatment for facilities where municipal infrastructure is unavailable or insufficient. We start with your wastewater: its flow, its load and what you want to do with the treated water. Our sewage treatment page has the enquiry form.
Request an application assessment with a Biozone engineer
It's free.
Call +27 67 972 2169 or +27 11 791 4403 · [email protected] · www.biozone.co.za
Frequently asked questions
Can treated sewage water be used for irrigation?
Treated wastewater can often be reused for non-potable purposes, including irrigation of landscaping and agriculture. Whether yours can depends on the quality the plant delivers, what you plan to irrigate and the requirements that apply. Treated sewage water is not drinking water.
What size of site is a modular sewage treatment plant for?
Biozone's commercial plants are designed for facilities generating 5 kilolitres a day and above, such as lodges, estates, schools, hospitals, shopping centres and remote infrastructure. Modular units let capacity follow the flow.
Why use ozone to disinfect treated sewage?
Ozone is a strong oxidant that reduces microbial contaminants and odours, and it can mean relying less on stored chemical disinfectants. Correctly engineered, it is designed to avoid leaving long-term chemical residuals in the water. It follows the biological and clarification stages, so that the water it treats is as clear as possible.
What is the difference between sewage treatment and wastewater treatment?
Sewage treatment deals with the wastewater from toilets, kitchens and washing in commercial facilities and developments. Wastewater treatment is the wider field, and it includes process and industrial water. Biozone's commercial sewage plants are built for the first; for specialised industrial wastewater, Biozone works with trusted engineering partners.
What does an application assessment involve?
Tell a Biozone engineer about your site, your flow and what you want to do with the treated water. The engineer will review your application and recommend the next steps. The assessment is free.
