Biodigester and Effluent for Dairy Plants and Cheesemakers
Whey and dairy effluent carry very high COD. How to treat them with an anaerobic reactor and recover biogas from whey in a turn-key plant by Tech Tank.
The effluent from a dairy plant or cheese factory carries very high COD from its lactose, fat and protein load: the general effluent runs 2,000–6,000 mg/L, but cheese whey is an extreme residue, with COD of 50,000 to 70,000 mg/L. Discharging it diluted is a costly mistake. The efficient route is anaerobic treatment, which removes most of the load and turns that energy into biogas, followed by aerobic polishing. Tech Tank integrates that plant turn-key with bolted steel tanks, a reactor and a gas holder.
The dairy effluent challenge
The dairy industry uses a lot of water in CIP cleaning, tank and equipment washing, and generates an effluent loaded with highly biodegradable organic matter. Load peaks appear with every cleaning cycle and with whey purges.
- Lactose: a very soluble sugar that drives up COD and acidifies the effluent.
- Fats and proteins: add load and form scums; they need prior handling.
- Cheese whey: the big problem and the big opportunity; COD 50,000–70,000 mg/L, an excellent biogas substrate.
- Variable pH: alkaline and acid CIP swing the pH; equalization and adjustment are needed.
- Intermittent flow: tied to production and cleaning shifts.
In Paraguay, discharge falls under MADES, Law 294/93 (Environmental Impact Assessment) and Law 3239/07 (Water Resources). It is worth verifying the current environmental license limits before sizing.
The Tech Tank solution: turning whey into biogas
The economic key is to stop seeing whey as a discharge problem and treat it as an energy substrate. Its high COD translates into a high biogas yield, and diverting whey from the general effluent immediately lightens the load on every downstream stage. That single decision often reshapes the whole plant balance, turning a disposal cost into an energy stream.
1. Equalization and pH adjustment
An equalization tank homogenizes flow, load and pH, absorbing the peaks from CIP cycles. Fats are separated when their content justifies it. This stage stabilizes the downstream anaerobic biology.
2. Anaerobic reactor + biogas from whey
The heart of the system. An anaerobic reactor (UASB or CSTR depending on the load) typically removes 70–90% of the COD of dairy effluent and generates biogas with 55–70% methane. Whey, thanks to its very high COD, is one of the best substrates: it can be co-digested with dairy manure to stabilize operation. The biogas is stored in a double-membrane gas holder and feeds boilers or generation.
3. Aerobic polishing and reuse
An aerobic treatment lowers residual BOD to meet discharge limits. With tertiary polishing, the water can be reused in non-potable uses. Tanks are bolted steel with glass-fused-to-steel coating (AWWA D103 and ISO 28765 standards), resistant to the aggressiveness of dairy effluent and CIP chemicals.
When the plant is linked to a dairy farm, the synergy is direct: see biodigester for dairy farms. The full-train engineering is delivered as a turn-key wastewater treatment plant, with the biogas and biodigester layer to capture the energy in whey.
Benefits with data
- Compliance: combined COD removal above 95% chaining anaerobic + aerobic.
- Energy from whey: instead of an environmental liability, whey produces biogas to replace boiler fuel and cut the plant's energy bill.
- Digestate: the digested effluent can be used as biofertilizer on nearby fields, closing the nutrient loop instead of paying to dispose of it.
- Modularity: bolted steel lets you grow with the plant's production.
Typical parameters by stream and stage
| Stream / stage | COD or function | Typical removal | Tech Tank equipment |
|---|---|---|---|
| General effluent | 2,000–6,000 mg/L | — | GFS equalization tank |
| Cheese whey | 50,000–70,000 mg/L | Biogas substrate | Anaerobic reactor + gas holder |
| Anaerobic reactor | Remove COD + biogas | 70–90% of COD | UASB / CSTR + double membrane |
| Aerobic polishing | Lower residual BOD | BOD < 50 mg/L (per license) | Bolted aeration tank |
The values are indicative; actual sizing depends on flow, whey volume and license limits. For a specific plant it is best to start from an effluent characterization. The Tech Tank team in Paraguay supports you from the initial technical consultation to commissioning.
Frequently Asked Questions
Why is cheese whey so problematic?
Because its COD (50,000–70,000 mg/L) is on the order of ten times that of a concentrated domestic effluent. Discharging or diluting it wastes energy and overwhelms any aerobic system. Treated in an anaerobic reactor, that same load becomes usable biogas, which is why keeping whey out of the general drain is the first design decision in any dairy plant.
Can you make biogas from whey alone?
Yes, whey is an excellent substrate, though it acidifies quickly. It is usually co-digested with dairy manure or another substrate to stabilize pH and reactor operation. Co-digestion improves the system's robustness and yield.
What is done with the digestate?
The digested material, rich in nutrients, can be used as biofertilizer on the farm's own or third-party fields, closing the nutrient loop. Its use must follow agronomic practices and the applicable environmental regulations.
What regulations apply in Paraguay?
Discharge is governed by MADES, Law 294/93 (Environmental Impact Assessment) and Law 3239/07 (Water Resources). The specific limits come from the plant's environmental license; we recommend verifying them with MADES before sizing.
Does it work for a small cheese factory?
Yes, the solution is modular. For smaller volumes a smaller reactor is sized or whey treatment as a substrate is prioritized. Bolted steel lets you start with what you need and expand as production grows, adding rings or units without replacing the original investment.