By Ruth Smith, Senior Design Manager Blue Projects
Tariff increases, reduced municipal capacity and tighter legislation are forcing those of us involved in food processing, brewing, and distilling, to integrate or retrofit efficient wastewater treatment processes into our own operations.
Companies sending their wastewater to municipal treatment facilities face stiff tariff increases based on volume, suspended solids and oxygen demand. Further pressure is added by reduced municipal capacity to treat effluent because of increasing domestic demand and aging and inefficient wastewater treatment plants. In addition, discharge to surface water bodies or rivers requires compliance to legislated limits, with restrictive limits on Nitrogen, Phosphorus and other compounds. Over and above sticking to the rules, we would be safeguarding and protecting our water resources for future generations.
Ideally, wastewater treatment is integrated into the design of the production facility. But all is not lost if it isn’t, solutions can also be retrofitted to existing sites with positive commercial results.
As a quick win, storm water should be separated from production effluent. If it is uncontaminated, the former can be directly discharged into the storm water system and water courses.
Remove Solids Early
Early removal of solids pays off by preventing blockages as well as combatting overloading of the downstream treatment system.
In food processes, fats, oils and greases (FOG) should be removed at source by grease interceptors. This will prevent pipe blockages and maintain the efficiency of downstream treatment processes. Grease interceptors must be cleaned and maintained regularly and the solid waste disposed of safely.
In brewing, solid material should be prevented from getting into the effluent drains in the first place. The culprits here are spent grains, broken glass and damaged labels. Screens and glass traps at strategic points in the production area act as effective barriers to effluent drains
The biological oxygen demand (BOD) of waste streams such as spent wash or traditional beer waste with a high solids content and high BOD, can be reduced by 40-45% by further dewatering at the next stage. Filter presses, decanters or settling are useful here. This step is worthwhile as a lower BOD reduces the scope and time required by downstream treatment processes.
For batch processes, particularly those with a cleaning step, a collection sump is advisable. This will help reduce the temperature and pH from cleaning processes. Fewer chemicals will be required for neutralisation and there is the additional benefit of buffering minor process deviations. For large scale problems, installing a calamity tank will protect the downstream biological processes.
Anaerobic or Aerobic Treatment
Depending on the results of the wastewater analysis at this point and the discharge targets, the wastewater will need either anaerobic (without oxygen) or aerobic (with oxygen) processing, or possible both. The table below summarises the parameters influencing the suitability of each process type:
Lean on the experts. Wastewater equipment providers and process design consultants will recommend specific technology solutions based on wastewater characteristics and discharge requirements.
If the discharge is to a water course, further removal of Nitrogen and Phosphorus maybe required as well as disinfection with chlorinated compounds or UV sterilisation.
Don’t walk away. The wastewater plant will not run itself. It requires consistent monitoring and management. There are compelling commercial reasons to keep your wastewater plant is operating properly. If it doesn’t, the whole production facility can be brought to a stand still and the company could hit the headlines for the wrong reasons.
We are convinced it is worth devoting time and attention to integrating wastewater treatment into the plant design, rather than adding it on as an afterthought.