An EQ tank can be a great solution for a medium sized brewery- or even large ones. This type of tank offers a lot of options at a low cost.
Like most living things, a wastewater treatment plant likes a steady state. A typical day of flow at the receiving end of a wastewater plant (called Headworks) will have a spike of flow between 6-8 AM or so as people take showers, make breakfast, etc. Then there is a drop in flow with a small spike around lunch time. Another drop, then a big spike as people get home from work, make dinner, do dishes, give kids a bath, etc. Then flow really drops off over night before the cycle starts again the next day. This is called diurnal flow, a famous exception to this is halftime of the Super Bowl. This type of variation is engineered in to the wastewater plant.
Most US wastewater treatment plants were built in the 1970’s, well before the craft beer revolution. A brewery has it’s own version of diurnal flow, usually with flow and load peaking during the work day and dropping off to zero overnight and weekends. Combined with the rest of the city’s flow, a graph of influent flow would look virtually unchanged with or without the brewery. However, depending on local conditions a graph of BOD and TSS load may look a lot different with and without the brewery, a spike with the brewery, no spike without. (See here for an explanation of load.)
One of the factors an EQ tank can help control is this diurnal flow. For instance the EQ tank can store wastewater produced during the day/week and discharge it overnight, or evenly 24/7. This levels out those spikes and that can be tremendously helpful to a small wastewater treatment plant.
Related to the above, another way an EQ tank can help is some municipalities will give a brewery a flow limit; possibly as low as 5 gpm! The EQ tank can absorb excess water in the head space of the tank and discharge to sewer at that constant rate- until the tank is empty or there is a high level alarm.
However the most common feature of an EQ tank is a place to do pH adjustment, manual or automatic. This type of system is commonly designed by Brewery Wastewater Design. We regularly design small EQ tank and pH adjustment systems. Often times the systems we design have the lift station, EQ tank, and pH adjustment all going on in one tank. It’s underground, out of the way, out of sight, saves space, and allows for expansion.
A helpful addition to an EQ tank is called a calamity tank. Read more about those types of tanks here. The general idea behind these tanks is if there is a spill in the brewery (beer, wort, chemical) you can isolate it in the calamity tank, then continue normal operations and dispose of the spill at a later date.