When it comes to wastewater management in Australia, understanding how different systems work is essential for homeowners, developers, and environmental professionals alike. One of the most important components in modern on-site wastewater treatment is the secondary treatment system. These systems go beyond traditional septic tanks, offering enhanced treatment of wastewater to ensure environmental safety and compliance with health regulations.

At Eco Septic, we specialise in Australian-made wastewater solutions that prioritise sustainability, reliability, and long-term efficiency. In this guide, we’ll break down everything you need to know about secondary treatment systems — what they are, how they work, the different types available, and why they might be the right choice for your property.

What is a Secondary Treatment System?

A secondary treatment system is a type of on-site wastewater treatment system that goes a step further than a basic septic tank. While septic tanks (primary treatment systems) separate solids from liquids and provide some anaerobic digestion, they do not adequately treat the liquid effluent. The wastewater leaving a septic tank still contains pathogens, organic material, and nutrients that can pose risks to public health and the environment if not treated further.

This is where secondary treatment comes in.

Key Features of Secondary Treatment:

• Further breakdown of organic matter

• Reduction of nutrients like nitrogen and phosphorus

• Removal of disease-causing bacteria and viruses

• Treatment of wastewater to a level safe for surface or subsurface irrigation

These systems use biological, mechanical, or chemical processes to improve water quality. In many areas of Australia, particularly where treated wastewater is to be reused or discharged into the environment, a secondary treatment system is a legal requirement.

Why Secondary Treatment Systems Matter

Secondary treatment systems are vital in reducing pollution and conserving our precious natural resources. With a growing population and increased strain on municipal sewer systems, decentralised wastewater solutions are becoming more important than ever.

Benefits of Secondary Treatment:

• Protects groundwater and surface water

• Reduces environmental contamination

• Allows for safe reuse of treated water for irrigation

• Improves public health

• Meets Australian compliance standards (AS/NZS 1546.3)

At Eco Septic, our secondary treatment systems are designed to be durable, efficient, and tailored to both residential and commercial applications. Let’s explore the various types of systems available and how they work.

Types of Secondary Treatment Systems

There are several types of secondary treatment systems used in Australia. Each has unique characteristics, treatment processes, and suitability depending on property size, soil type, and wastewater volume.

1. Aerated Wastewater Treatment Systems (AWTS)

AWTS are one of the most commonly used secondary treatment systems in rural and semi-rural Australia. These systems mimic the processes used in municipal sewage treatment plants but are scaled down for individual households or small communities.

How it works:

AWTS typically involve four to five chambers:

1. Primary Chamber – Receives raw sewage and separates solids.

2. Aeration Chamber – Introduces oxygen to promote aerobic bacteria that digest waste.

3. Settling Chamber – Allows any remaining solids to settle out.

4. Disinfection Chamber – Treated with chlorine or UV to kill pathogens.

5. Irrigation Pump Chamber – Pumps treated water for reuse.

Pros:

• High treatment efficiency

• Produces reusable water for irrigation

• Complies with most council regulations

• Compact design suitable for homes and small businesses

Cons:

• Requires quarterly servicing

• Needs power to operate

• More complex than basic septic systems

Eco Septic’s AWTS units are Australian-made and engineered for long-term performance. Our concrete tank designs are environmentally friendly and blend seamlessly into your landscape.

2. Sand Filter Systems

A sand filter system uses a bed of specially graded sand to biologically treat wastewater after primary treatment. Effluent from a septic tank is filtered through the sand, where aerobic bacteria break down organic matter.

How it works:

• Wastewater from the septic tank is distributed over a sand bed

• It slowly trickles through the sand layers

• Bacteria on the sand grains digest waste

• Treated water is collected and dispersed into the soil or used for irrigation

Pros:

• Low-energy system

• Simple and reliable

• Long lifespan with proper maintenance

Cons:

• Requires a larger land area

• Filter media may need periodic replacement

• May not suit clay soils or steep slopes

Sand filters are ideal for environmentally sensitive areas and properties with ample space. They offer effective secondary treatment without mechanical components.

3. Subsurface Flow Constructed Wetlands

Constructed wetlands use natural processes involving wetland plants, soils, and associated microbes to treat wastewater.

How it works:

• Effluent flows horizontally through a gravel bed planted with wetland vegetation

• Bacteria on the plant roots and gravel break down nutrients and pathogens

• Water is treated naturally and safely dispersed

Pros:

• Low-maintenance and energy-efficient

• Aesthetic appeal with natural vegetation

• Sustainable and environmentally friendly

Cons:

• Requires a large area

• May take time to establish plant growth

• Performance can vary with weather conditions

Eco Septic supports eco-friendly innovations like constructed wetlands for customers looking for a greener solution.

4. Textile Filter Systems

These systems use textile material (often synthetic or natural fibers) as a medium through which effluent flows. Like sand filters, they rely on aerobic bacteria to digest organic matter.

How it works:

• Septic tank effluent is applied intermittently to the textile media

• Microbial action treats the wastewater

• The treated water is collected and sent for final disposal or reuse

Pros:

• Compact design

• Effective treatment with minimal space

• Easy to install in restricted sites

Cons:

• Media may need replacement over time

• Higher initial cost than sand filters

This system is useful for locations where space is limited but high-quality treatment is needed.

5. Membrane Bioreactor (MBR) Systems

Membrane bioreactors combine biological treatment with advanced filtration technology. These are more advanced systems suited for commercial or high-end residential use.

How it works:

• Aerobic biological treatment occurs in one chamber

• Effluent passes through a membrane filter

• The result is crystal-clear, high-quality water suitable for reuse

Pros:

• Very high treatment standards

• Compact and efficient

• Low pathogen and nutrient levels

Cons:

• High initial investment

• Requires electricity and regular maintenance

At Eco Septic, we typically reserve MBR systems for commercial or multi-residential projects where the highest level of treatment is required.

Comparing the Different Systems

Choosing the Right Secondary Treatment System

Selecting the appropriate system depends on several factors:

• Site Conditions (soil type, slope, available space)

• Water Table and Environmental Sensitivity

• Household or Business Wastewater Load

• Budget and Maintenance Preferences

• Council or Regulatory Requirements

At Eco Septic, we offer tailored site assessments and design recommendations to ensure you choose a wastewater solution that meets your needs — both now and into the future.

Why Choose Eco Septic?

We’re more than just a wastewater system supplier. We’re passionate about sustainable Australian-made solutions that support a cleaner, greener future.

• ✅ All systems made in Australia

• ✅ Built to exceed AS/NZS standards

• ✅ Custom-made options available

• ✅ Full service and maintenance programs

• ✅ Ongoing support from our expert team

We supply secondary treatment systems to homeowners, developers, and commercial operators across NSW, Victoria, ACT, Queensland, and Tasmania. Whether you’re building a new home off the grid or upgrading an outdated septic system, we’re here to help.

Secondary treatment systems are an essential part of modern wastewater management. They offer improved environmental protection, meet stringent health and council regulations, and allow for safe water reuse. With several options available — from AWTS and sand filters to constructed wetlands and MBRs — there’s a solution for every property and every purpose.

At Eco Septic, we pride ourselves on helping Australians find the right wastewater system with quality they can trust. If you’re ready to upgrade your septic system or need help choosing the right secondary treatment solution, our team is here to guide you through the process.