Aerobic treatment needs oxygen, so aeration makes it a net energy consumer. Anaerobic treatment works without oxygen and turns the organic load into biogas, typically yielding four to seven times more energy than an aerobic plant uses for aeration at the same load. It also produces five to ten times less sludge. Exact figures depend on wastewater composition, temperature and plant design.
Anaerobic treatment becomes economically attractive above roughly 2–3 tonnes COD per day, where biogas revenue and avoided aeration power offset the reactor investment. Below that, aerobic treatment alone is usually cheaper. The threshold also depends on conditions: warm wastewater (above 30°C) and low toxicity favour anaerobic treatment.
High-rate anaerobic treatment uses reactors that retain granular sludge separately from the water, so wastewater flows through quickly while the bacteria stay inside. This allows high organic loads in a compact footprint. It is the right choice for soluble, high-strength wastewater, such as food and beverage effluent, with low suspended solids and FOG (fats, oils and grease) content.
An anaerobic MBR adds membrane separation to anaerobic treatment, retaining biomass completely and producing a particle-free effluent. It suits effluents that will not granulate (typically high-fat, high-solids or variable streams) and sites where the effluent is intended for reuse. Capex and membrane cleaning costs are higher than for a granular reactor.
Mesophilic reactors run best at 30–38°C. Below 30°C conversion rates fall sharply and reactor volume must grow, so heating with recovered biogas is usually cheaper than oversizing. Many food and beverage effluents arrive warm enough that no external heating is needed.
An EGSB (Expanded Granular Sludge Bed) is a more intensive evolution of the UASB. Its high upflow velocity expands the granular bed, improving contact between bacteria and wastewater. EGSB handles 15–30 kg COD/m³/day in a compact, tall reactor, ideal for soluble effluents such as brewery wastewater. UASB handles 5–10 kg COD/m³/day but tolerates solids and fats better.
GWE’s ANUBIX™-T EGSB reactor turns high-strength wastewater into energy rather than cost. Its granular sludge achieves low effluent COD/BOD, so only a small aerobic polishing stage is needed, and it produces far less excess sludge than aerobic treatment. With no moving parts inside, maintenance and downtime are minimal, while the biogas produced can replace natural gas.
It is the first treatment step in wastewater treatment. It removes solids, fats, oils and grease before the water goes to biological treatment.
GWE offers two main technologies: SUPERFLOT™ and SUPERSEP™. SUPERFLOT™ is a dissolved gas flotation system, it comes in 2 versions: AIR or GAS. SUPERSEP™ handles solid-liquid separation and comes in a Crossflow lamella-type solids separator and a Downflow lamella separator.
Fats, oils and grease are removed in a primary treatment step, ahead of biological treatment. Grease traps and gravity separators suit small flows; for industrial wastewater, dissolved air flotation (DAF), often with coagulant dosing, is the standard. Removing FOG protects pumps, membranes and biomass, while recovered fat can be digested for extra biogas.
Every water stream needs a tailored combination of technologies. GWE designs and builds complete treatment trains, drawing on proven experience in membrane filtration (ultrafiltration, nanofiltration and reverse osmosis), chemical water treatment and disinfection.
Ultrafiltration removes suspended solids, bacteria and most colloids, and is often enough for cooling, make-up and washdown. Reverse osmosis additionally removes dissolved salts and is needed for boiler feed, product-adjacent reuse or where the effluent is saline. RO adds a concentrate stream that must itself be managed.
The EU Water Reuse Regulation (2020/741), applicable since 26 June 2023, sets minimum requirements for reusing treated urban wastewater in agricultural irrigation. Industrial water reuse is mainly governed through permit conditions under the Water Framework Directive and Industrial Emissions Directive, which each Member State applies in its own way. Link: Water Reuse - Environment - European Commission
Biogas is produced through anaerobic digestion. After pre-treatment removes solids and fats, wastewater enters an oxygen-free reactor where microorganisms break down the organic load in four steps: hydrolysis, acidogenesis, acetogenesis and methanogenesis. The resulting biogas, a mix of methane and CO₂, is collected, cleaned and used for heat, electricity or biomethane. The treated water then goes on to polishing or reuse.
Once cleaned, biogas becomes a valuable on-site energy source. It can fuel boilers for process heat, a CHP unit for electricity and heat, or be upgraded to biomethane. This lowers energy costs, reduces dependence on fossil fuels and cuts the carbon footprint. For high-strength effluents, it can cover most or even all of a site’s energy needs.
Each kilogram of COD removed theoretically yields 0.35 m³ of methane (at 0°C, 1 atm). Biogas is about 60–65% methane, so that equals roughly 0.55 m³ of biogas per kg COD. Example: 10,000 kg COD removed per day × 0.35 = 3,500 m³ methane, or about 5,500 m³ biogas (≈35 MWh/day). Actual yields depend on wastewater composition and the final plant design.
Biogas contains hydrogen sulfide (H₂S), which corrodes engines and pipes. The main removal technologies are biological desulfurization (bacteria and air), iron salt dosing in the digester, chemical scrubbers, and adsorption on activated carbon or iron oxide. Many plants combine bulk removal with a final activated carbon polish. The best choice depends on H₂S load, gas flow, end use and operating cost.
Capex depends on load and discharge limits, not on flow alone. A complete anaerobic–aerobic plant for a mid-size food factory typically costs between €2 and €3 million. The final cost depends on whether the effluent is diluted or concentrated, the daily capacity, the type of installation, whether reuse is required and local electromechanical and civil works costs.
From signed contract to commissioned plant is typically 12–18 months for a complete anaerobic–aerobic installation. This includes several months of detailed engineering, six to nine months of manufacturing and construction, and two to four months of start-up. Permitting often runs in parallel and can be the critical path.
Buying outright gives the lowest lifetime cost but requires in-house operators. Alternatively, Ekopak-GWE offers DBFMO (Design, Build, Finance, Maintain, Operate), known as Water-as-a-Service (WaaS®): Ekopak-GWE owns and operates the plant, and the customer pays per m³ treated water. No capex, no performance risk: ideal for sites without water-treatment staff or budget.
Often, yes. GWE first audits the existing plant to assess the options. Overloaded aerobic plants are frequently rescued by adding anaerobic pre-treatment ahead of them, which removes most of the load and frees the existing capacity for polishing. Where footprint rather than load is the constraint, existing tanks can be converted to MBBR or MBR.
Reuse pays where water tariffs, discharge fees or supply reliability are the binding constraint. Because tariffs and regulations differ by country, the business case varies. Rising tariffs, abstraction limits and corporate water targets typically bring payback on a reuse system to three to six years, before counting the value of production continuity in a drought.
