High-COD effluent is a fuel bill, not a disposal bill

There is a specific moment on a lot of industrial sites when the treatment plant stops being a compliance item and becomes a line on the energy report. It happens when the organic load gets high enough that the aeration blowers run continuously.

The problem with destroying organics aerobically

Aerobic biological treatment works by giving bacteria oxygen and letting them oxidise the organic load. The oxygen has to be blown in, continuously, and blowing air into water is expensive. Worse, the process converts a substantial fraction of the organic load into new biomass — sludge — which then has to be thickened, dewatered and hauled away at further cost.

So a high-COD effluent generates two large operating costs simultaneously: the electricity to destroy the load, and the disposal cost of the sludge that destroying it creates.

What anaerobic membrane treatment changes

AnaeroMBR combines a completely mixed anaerobic reactor with low-energy tubular ultrafiltration membranes. Anaerobic bacteria convert the organic load to methane instead of to biomass and carbon dioxide, and the membrane holds the biomass in the reactor rather than relying on it settling.

The numbers that follow from that:

• Up to 98% COD removal, giving effluent quality ready for discharge or reuse.
• Energy use of 1.5–2.5 kWh per cubic metre of net permeate output, with no aeration, no flocculants and no gas scouring — and biogas produced against that, making the process net energy positive.
• Up to 75% less sludge than an aerobic process.

Why the membrane matters more than the biology

Conventional anaerobic systems — UASB and EGSB reactors — depend on granulation to keep biomass in the reactor. Granulation is fragile. Fats, oils, grease, salinity and toxic compounds all disrupt it, which is why conventional anaerobic treatment has a reputation for being difficult on real industrial effluent.

Holding the biomass with a membrane instead removes that dependency. The comparison is stark: AnaeroMBR tolerates a COD load above 250 g/L, against under 15 g/L for a conventional anaerobic system and under 10 g/L for an aerobic MBR. TSS and FOG tolerance is very high rather than low. Pre-treatment needs are minimal rather than high. Start-up is short rather than long, because no granular seed is required.

The maintenance argument

The membrane units sit outside the tank — external and dry — rather than submerged. That means inspection and replacement without confined-space entry and without draining the reactor. Membrane durability is specified at eight years.

Anyone who has organised a submerged membrane change-out on an operating plant will recognise why this matters more than a percentage point of flux.

Where it fits

Food and beverage effluent, particularly dairy, brewing and starch. High-COD chemical and petrochemical streams. Pulp and paper. Pharmaceutical production effluent. Agricultural and agro-processing waste. And sludge-to-energy schemes at municipal works.

Where it does not fit is dilute effluent. Anaerobic treatment needs organic load to work with; below a certain strength, the biogas does not justify the plant and aerobic treatment is simply cheaper.

The question to ask

Not "what does the treatment plant cost". Ask what your aeration electricity costs per year, and what your sludge disposal costs per year, and add them together. On a high-strength effluent, that number is often larger than anyone in the building realises — and it is the number that anaerobic treatment is designed to attack.