A Multi-Tiered Approach to Sanitation
Large municipal sewage treatment works are the backbone of South African sanitation, with approximately 12 million households connected to a municipal sewer. However, these systems are taking strain.
According to the 2023 Green Drop Report, 334 of South Africa’s 850 municipal plants are in a critical state. These facilities often face the dual challenges of being hydraulically overloaded and contending with maintenance backlogs. As a regulatory response to protect the integrity of our water systems, the DWS has, in several regions, restricted additional bulk sewer connections to plants that lack the surplus capacity to treat new influent.
This can effectively delay residential, commercial and industrial infrastructure developments, as the upgrade of large municipal sewage treatment works is complex and can take a couple of years to come online.
With the current pressure on the grid, small-scale onsite sewage treatment plants can present an alternative to bridge the gap.
Onsite Wastewater Treatment vs. Municipal Sewage Treatment Plants
What Is the Difference Between a Sewage Plant and an Onsite Wastewater Treatment Plant?
A municipal sewage treatment plant is a large, centralised facility that receives wastewater via extensive pipeline networks, while an onsite wastewater treatment plant treats sewage directly where it is generated. Municipal works serve high-density areas and operate at large daily capacities, whereas onsite systems are smaller, decentralised, quicker to deploy, and ideal for locations without municipal sewer availability.
Large centralised municipal sewage plants rely on an extensive network of large-bore pipelines and pumping stations to convey the untreated sewage to a centralised plant with a substantial footprint, generally outside of the city. The treatment capacity is typically between 50 000m³ to 4,2 million m³ per day in the South African treatment network. The treated effluent is discharged back into the natural water system. The treatment works are sophisticated with full-time process controllers and automation and control plant systems.
A small-scale sewage plant on site treats effluent where it is generated. The capacity is between 1m³ to 250m³ per day. The onsite treated effluent (meeting National Water Act general limits) is perfect for irrigation, dust suppression, and non-potable reuse, keeping the water within the local ecosystem.
The difference between a municipal sewage plant and an onsite wastewater treatment plant isn’t just about size; it’s about application. While bulk connections are ideal for high-density urban nodes, small onsite wastewater treatment plants in South Africa allow for development in areas where the municipal grid is at capacity or geographically unreachable.
Engineering Integrity, Maintenance, and Compliance
Calcamite’s approach to decentralised wastewater treatment systems is built on the same foundational engineering principles that govern large municipal sewage treatment works, ensuring that our onsite solutions are both technically robust and fully compliant.
1. Design Based on Industry-Standard Engineering Principles
Our systems are not “black box” solutions; they are engineered based on globally recognized methodologies. Calcamite’s design framework incorporates principles from Metcalf & Eddie and WRC (Water Research Commission), and Water Environment Foundation reports.
We utilize a multi-stage continuous flow process designed to meet the specific effluent requirements of the National Water Act:
- Primary Treatment: Robust solids separation and settlement.
- Biological Nutrient Removal (BNR): Utilizing anoxic zones for denitrification and aerobic bioreactors for COD reduction and nitrification.
- Advanced Aeration: Our bioreactors maintain dissolved oxygen levels (typically 4–6 mg/l) to ensure high-rate nitrification, crucial for meeting General Limit standards.
- Secondary Clarification & Disinfection: Precise up-flow velocity calculations for settlers and scientifically determined contact times for chlorine or ozone disinfection.
2. Proven Track Record and Deep Field Experience
Engineering specifications are only as good as their real-world application. With 1,891 plants treating a combined 2.3 million m³ per annum in the field, Calcamite brings a wealth of empirical data to every new project. This extensive footprint allows us to understand the nuances of various influent strengths, from high-density residential estates to the unique loads found at remote mining sites and game lodges.
3. Professional Oversight and Process Control
Compliance is a dynamic process, not a static event. The Department of Water & Sanitation (DWS) requires a formal maintenance plan to be submitted with every Water Use License Application (WULA). Calcamite supports this requirement by providing:
- Professional Process Controllers: Our team includes qualified controllers who oversee all maintenance activities and ensure that the biological health of the system is optimized.
- Regulatory Compliance: We ensure that the plant consistently meets the effluent standards determined by the site’s specific water use license.
4. Daily Remote Monitoring and Proactive Control
To further mitigate risk for both the engineer and the end-user, Calcamite offers plants equipped with remote monitoring and control systems.
- Real-Time Data: Our Aveva Connect/Schneider Electric integrated systems, implemented by 4Sight Automation and Control, allow for the daily monitoring of critical parameters.
- Proactive Maintenance: Our professional process controllers review this data daily. If a variance is detected, a maintenance team is deployed immediately, often resolving a potential issue before it affects effluent quality.
- Reduced Operational Burden: This “smart” oversight ensures that maintenance is not onerous for the client while providing the engineer with the peace of mind that the design is performing as specified.
Conclusion: Unlocking Development Through Partnership with Calcamite
In the current South African landscape, the path to a successful development often requires navigating complex infrastructure hurdles. While large municipal sewage treatment works remain the ultimate goal for urban densification, decentralised wastewater treatment systems provide the agility needed to move projects forward today.
By integrating a small onsite wastewater treatment plant into your design, you aren’t just solving a sanitation problem, you are unlocking the potential for new residential estates, hospitals, and commercial hubs that would otherwise remain stalled.
