Only a small portion of BOD can be filtered or removed from brewery wastewater. Options are to not put it down the drain in the first place, treat it, or have someone else treat it for you. Let’s talk about not putting it down the drain in the first place- we’ll call it side streaming.
Side streaming is collecting high strength, concentrated wastes at the source and setting it aside for disposal. Primary sources of this high strength wastewater are trub and spent yeast. Smaller sources would be fermenter bottoms, returned beer in kegs, fermenter blow off, and beer in hoses or pipes at the beginning or end of a packaging run. In the brewhouse they would be lauter tun rinsings, hop back rinsings, and any kettle residues. Collect it all, put it in a tank (outdoors, in back, it’ll stink), and spread it on pastures as fertilizer- or even feed it to animals. You could have 1 big tank or you could find used chemical totes (IBC’s); doesn’t need to be fancy. It can go on the fields as is, solids and high temperature are OK. If feeding it to animals make sure you are indemnified against any misuse of this product by the hauler/farmer; spent yeast can cause bloat and drunkenness. Generally the fertilizer content of this material is lower than the cost of hauling, so you may have to pay for hauling. Concerns with land application are runoff to surface water and over application of nitrogen. I feel like I’m stating the obvious here, but do not go to the field and open a valve and dump it all in one place. Drive/move as it’s being spread so it is being applied thinly, and only apply to the same piece of ground 2x per year…
Of course, spent grain should be your first side stream. You might even decide to add your trub and spent yeast in here? Spent grain does have value as feed, at a minimum you can give it away in exchange for the farmer promptly hauling it away. Maybe you can get some free beef out of the deal? Larger breweries should be able to sell their spent grain. The value of spent grain increases as moisture content decreases; 80% moisture is a great target. Read more about spent grain here, it’s a good read.
After side streaming, the remaining portion of your wastewater can be referred to as process wastewater. This will be cleaning and CIP water in your cellar and brew house as well as any packaging line wastewater, boiler and cooling tower blow down, and general wash down waters. Sanitary wastewater (toilets, sinks) should not be included in this waste stream and should be piped directly to the sanitary sewer or facility.
One technique I have not tried is to add CIP water to your side stream. What this accomplishes is you don’t get pH spikes in your process wastewater. The side stream material is concentrated and acidic and will neutralize the caustic CIP waters. Salinity will increase with this method, which may be of concern in places like California.
You could opt to treat the wastewater on site at your brewery. If the town you are in is tiny, the treatment plant is at capacity, or if there is no municipal treatment plant you may be forced to treat. But ask yourself, what business are you in? Making beer or treating wastewater? Treating wastewater is expensive business. Aerobic treatment methods feature the cheapest capital costs but have higher operating costs. Remember those blowers I talked about earlier? Anaerobic treatment options have higher capital costs but lower operating costs. Either method will require require significant time, money, and space. You can also run into the problem of having to brew to feed your wastewater system- tail wags the dog so to speak. Not the best business model. In general terms, and this can change based on new technologies, anaerobic treatment does not make economic sense for a brewery until close to 200,000 bbls/year gross production. Go here to read more about more brewery wastewater treatment opinions and options.
The best option is almost always to have someone else treat your wastewater for you- especially if they’ll do it for free. Doing what you can to make the people at your municipality happy to treat your wastewater for you is a great deal. My best piece of advice for any brewer may be to ‘play nice’ with the regulatory authorities you have to deal with. They may give you rules, laws, and limits to abide by, as well as charge fees- and you might not agree with them all. But smile, be courteous, professional, and try to see things from their perspective. Do not get in to an adversarial relationship. They have lawyers on retainer and they probably know their laws better than you do. All of this doesn’t mean don’t try to negotiate- just be professional. They can treat your wastewater cheaper than you can, they have a better tolerance for low payback projects, plus they already have the rate-payer funded equipment and staff.
A story I am aware of is a brewery installed an anaerobic treatment system, part of the justification was current natural gas prices. As we’re all aware natural gas prices fell, and the brewery is generating biogas at a higher cost than they can buy natural gas. Biogas is greener for sure, but we’re all in business and economics rule the game. Another part of their justification was public perception and doing the right thing. Over time they learned memories are short, not many people will support a business based solely on sustainability, and sustainability gets harder to communicate as a brewery moves farther afield.