I had a request to see if a low cost biological pretreatment system could lower POTW surcharges and meet permit requirements for an expanding facility that dewaters portable toilet wastes. This waste has a high organic concentration with an influent COD 6,000 mg/L. Additional concerns include hydrogen sulfide and other odor causing compounds.
The facility has limited space for a biological treatment unit and does not want to incur extensive capital expenditure. A initial bench study was done over a 10 hour period to determine if biological treatment could reduce COD.
First the bench test was done using bioaugmentation cultures designed for high COD wastewater – the microbial seed included organisms selected from Bacillus, Pseudomonas, and Rhodococcus species. Preserved in a dry form, we decided to not pre-acclimate or revive the product before adding to the inlet sample.
Temperature was approximately 23 Deg C during the test. Aeration and mixing were provided with a normal aquarium airstone & pump.
We pulled samples at time 0, 6, & 10. This is because the maximum HRT we can realistically have on the site is 12 hours.
One issue is that it takes at least 4 hours for the cultures to “revive” and acclimate to the waste. Therefore, kinetics from this run are not suitable for eventual prediction of how well the system will run. In a working system, there is always an active biological portion that is kept after discharge when a pretreatment system is operated in batch mode. The expected design is an aerated tank (possibility of adding fixed media will be considered), with additions of bioaugmentation cultures during periods of high flow, difficult temperatures, and when loadings have variation.
The initial results from COD tests are presented in the figure below. During the 10 hour test COD decreased from 5,900 mg/L to 3,400 mg/L.
While I ran a regression on COD reduction versus time, the only reliable conclusion from this test is that the waste is treatable using aerobic biological pretreatment. A second set can be done with an acclimated biomass (give at least 48 hours on aerated waste influent). From this 48 hour aerated flask, discharge 75% of the waste and recharge with fresh influent. Take samples at time 0, 4, 8, and 12 hours.
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
Click to set custom HTML