The Problem :
The wastewater treatment plant for a medium-sized food factory produced a lot of anaerobic odours and generated poor quality final effluent which did not meet EPA discharge licence limits for BOD, COD, solids and pH. The system was an aerobic 'draw and fill' type biological plant, which worked in a semi-batch fashion, treating water in a cycle of aeration, settling and decant.
The Process :
(a) Sampling and Analysis:
Ex-factory and ex-wastewater plant effluent was sampled on a daily basis over a 2 week period using autosamplers. The pH into and out of the wastewater plant was also measured on an hourly basis. The collected samples were analysed in a laboratory for BOD, COD and suspended solids.
All of the results were combined to generate an accurate profile of the wastewater across the treatment system over the course of a typical 2-week factory production cycle. The average and maximum pollutant loading was calculated from this data, using daily outfall hydraulic flow figures.
(c) Profile Conclusions:
Comparison of the various analysis results showed a system which was heavily overloaded with respect to all pollutants. However pH was fairly stable across the system. It was also found that the existing aeration capacity was well short of requirements and the ex-factory effluent contained large quantities of non-biodegradable materials.
(d) Bench-scale Trials:
Laboratory-scale trials were carried out to determine whether digestion of previously refractory (non-biodegradable) pollutants was possible, using a number of different proprietary Bichem bacterial culture.
(e) Trial Conclusions:
The trials were found to be very successful in breaking down most of the refractory COD into BOD and then into C02 + water. Digestion of the more biodegradable BOD materials was also improved, as was the settling out of the biomass.
It was recommended that the aeration system be upgraded to allow for the complete degradation of all pollutants to well below licence limits. The recommended upgrade was determined using load calculations obtained from the profile (see above) and from the laboratory trials.
A well known and respected aeration equipment supply company known as PCPL P/L was used to provide the upgrade to the blower and diffusers in the aeration tank.
It was also recommended that once the upgrade was commissioned, the aeration tank should be seeded with the most successful bacterial culture blend as determined by the laboratory -scale trials.
Final Outcome :
After installation of the new aeration system and re-seeding with Bichem the odours previously associated with the treatment plant disappeared entirely and the biomass turned a healthy brown colour. The new diffuser system provided an ideal environment for growth of the bacterial cultures and the final effluent rapidly became clear and well below licence discharge limits for all parameters.
Ongoing Monitoring and Consultancy :
Since this time the plant has continued to function well, with Aquadynamic Consultancy Services monitoring the system on a monthly basis and making recommendations and adjustments to plant operation as required.