Trade Waste Systems

Trade waste systems treat liquid waste from commercial and industrial activities before it enters the public sewer, so fats, oils, solids and chemicals do not block sewers or harm treatment plants. They are governed by agreements or consents with the water utility that set what may be discharged, how it must be treated, and how often treatment devices must be emptied and sampled.

Most arrestors are concrete, steel or plastic tanks in the ground or in basements, with baffles that slow the flow so grease floats and solids settle. They work only if they are sized for the flow and emptied before they fill. When a tenancy changes from a café to a high-volume restaurant, the arrestor that served the café can be overwhelmed.

What shortens life:

• Infrequent pump-outs, which leave acidic, septic waste in contact with concrete and steel for long periods.
• Hot water and chemical cleaners discharged into arrestors, which carry grease straight through and attack the tank.
• Traffic loads on covers not rated for vehicles.
• Undersizing for the current use, so devices are overloaded continuously.

Overload and undersizing

An arrestor sized for a small café cannot treat the flow from a commercial kitchen. Grease passes through to the sewer, blocking the building's drains and the public sewer, and the utility issues notices or fines. Food court and multi-tenancy buildings often have shared arrestors whose capacity was set for an earlier tenant mix.

Missed pump-outs

Arrestors must be emptied at a frequency set by the utility or the agreement. When pump-outs lapse, grease and solids fill the tank, overflow to the sewer, and turn septic and odorous.

Corrosion of the tank

Hydrogen sulphide and acids from decomposing waste attack concrete above the liquid line and corrode steel baffles and fittings. Corroded baffles let grease pass straight through; failed walls leak into the ground.

Bypasses and wrong connections

Dishwashers, floor wastes and sinks connected around the arrestor, or arrestors bypassed after blockages, discharge untreated waste. Connections added in fit-outs are a common source.

Odour and gas

Septic arrestors release odours into kitchens, basements and public areas through failed seals and lids. Hydrogen sulphide makes arrestor pits dangerous confined spaces.

Cover failures

Covers in car parks and service lanes crack and break under vehicles, creating trip and fall hazards and letting stormwater in.

Oil interceptor faults

Oil interceptors fill with oil and silt, alarms fail, and coalescer media clog. A full interceptor discharges oil to the sewer or stormwater system, which is an environmental offence.

On site

• Arrestor location, size and covers; odour around lids.
• Fat build-up in kitchen drains and frequent blockages downstream of kitchens.
• Pump-out labels or dockets; date of the last service.
• Oil interceptor alarms and level indicators.
• Cracked or rocking covers in trafficked areas.
• Dishwashers and floor wastes connected directly to the sewer.

In the records

• Trade waste agreement or consent with discharge limits.
• Pump-out dockets and frequency.
• Utility notices, sampling results and fines.
• Tenant kitchen specifications.
• Drain blockage history.

• Kitchen staff pouring fat, oil and food scraps into sinks rather than collecting them, a management issue that overloads even well-sized arrestors.
• Sewer overflows or utility crews attending blockages in the street outside the building.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator or ordinance sets the date), check (investigate before sizing works) and nil (cosmetic or stable).

A hydraulic engineer or licensed plumber with liquid waste contractor support; confined space procedures for entry.

• Inventory of every pre-treatment device, its size, material, age and what it serves.
• Capacity check of each arrestor against the current kitchen fixtures, meals and flow, using the utility's sizing method.
• Internal inspection after pump-out: walls, baffles, inlet and outlet fittings, seals and covers.
• Connection survey by dye testing to confirm every fixture that should discharge through the arrestor does, and nothing bypasses it.
• Records review: trade waste agreements, pump-out frequency against requirements, utility sampling and notices.
• Oil interceptor checks: levels, alarms, media and outlet condition.
• Cover load ratings against the traffic over them.

The report should state compliance with the utility's requirements, capacity against current use, condition, bypasses, and the works and pump-out frequency needed.

• Pump-out regime set to the utility's requirement and the actual loading, with dockets kept on site.
• Upsizing or additional arrestors where tenancies have outgrown the existing devices, usually as a condition of the new tenancy.
• Internal repair: replace corroded baffles and fittings; reline concrete tanks with acid-resistant linings.
• Replacement with plastic or fibreglass units where concrete or steel tanks have failed.
• Connection corrections: route dishwashers, floor wastes and sinks through the arrestor and remove bypasses.
• Heavy-duty covers rated for the traffic, with gas-tight seals.
• Oil interceptor servicing: emptying, media replacement and alarm repair.
• Tenant obligations: lease clauses requiring tenants to maintain their devices and fund upgrades their use requires.

Pump-outs recur at the required frequency and are usually a tenant or service charge cost. Internal repairs and relining are lump sums per device. Replacement or upsizing is a lump sum including excavation in kitchens, basements or car parks, which can disrupt tenants. Utility fees and fines are operating costs that capital works avoid. Cover replacement is per cover.

Utility-required upgrades carry deadlines; replacement is lifecycle; pump-outs and repairs are repairs and maintenance; tenant-driven upsizing should sit with the tenancy.

• Australia. Water utilities set trade waste requirements through agreements or permits, with arrestor sizing, pump-out frequencies and sampling (for example Sydney Water and the Melbourne retailers); AS/NZS 3500.2 governs the plumbing; confined space entry follows AS 2865.
• United Kingdom. Discharges of trade effluent need consent from the water company under the Water Industry Act 1991; grease separators follow BS EN 1825 and light liquid separators BS EN 858; local authorities enforce on food premises where fats block sewers.
• United States. Local pretreatment programmes under the Clean Water Act and municipal fats, oils and grease ordinances set requirements; plumbing codes set grease interceptor sizing; oil separators follow local and environmental rules.

Lease terms matter in all three jurisdictions: in multi-tenant buildings, the agreement is often in the owner's name while tenants generate the waste, so leases should allocate pump-out, upgrade and fine costs to the tenant whose use requires them.

• Trade waste agreements, permits or consents, with discharge limits.
• Pump-out dockets for the last two years.
• Utility notices, sampling results and any fines.
• Drawings showing arrestors and the fixtures connected to them.
• Tenant kitchen fit-out specifications.
• Drain blockage history downstream of kitchens.
• Oil interceptor service and alarm records.