I am happy to report the findings of my R&D to help lakes reduce the impact from septic systems. The alum conditioning system I developed has worked flawlessly after 4 1/2 years of testing. There have been a number of significant results to report, all of which support the original goal of minimizing phosphorus discharge to the disposal field and maximizing collection within the septic tank. Thus, alum treatment of household wastewater from an ordinary home was found to improve the basic function of the septic tank’s separation and settling capability and reduce the load to the disposal field. I found that a single tank system with a capacity of 1000 gallons, can remove over 90% of the soluble phosphorus found in an untreated wastewater system at an average alum feed of 260mg/liter of wastewater. The 1000 gallon tank total phosphorus removal was 60-70%. Approximately 30-40% of the suspended solids was in the form of aluminum phosphate, an insoluble compound of the aluminum phosphorus reaction and not available to ground water or absorption. From a disposal field perspective, the “system” removed over 90% of the phosphorus.
Sampling after the 500 gallon tank revealed further settling of the precipitate had occurred to increase the total removal of phosphorus to 80%. As previously stated, the aluminum and phosphorus leaving the 500 gallon tank were insoluble precipitate of aluminum phosphate and that the total phosphorus removal of the system (tanks and field capture) was over 90%.
An added and important benefit of this system was the ability of alum treatment to remove over 92% of the total coliform in the tank. The exact mechanism is not clear, but is thought to involve the alum floc’s ability to absorb bacterial components. The average total coliform before alum treatment was 2.5 x 10*6 counts per 100ml. After alum treatment, the average coliform was 1.98 x 10*5. This means that only 8% of total coliform leaves the tank. A reduction of this amount of bacteria will benefit the infiltration zone of the disposal field and reduce potential clogging, and minimize potential pathogens to the environment.
Over 3 1/2 years of alum treatment, with most of that time at a high alum feed rate of 400mg/liter to artificially accelerate sludge accumulation, the tank maintained an average sludge level of 12-13 inches throughout 3 years 4 months. This strongly implies that alum has no deleterious affect on organic digestion. The pH of the sludge ranged between 6.2 – 6.6. The sludge accumulation of an untreated (with no alum) 1000 gallon tank over 3 years was 8 inches. The affect of the alum treatment resulted in about 4 inches greater sludge depth. Throughout the duration of the 3+ year test, approximately 50 gallons of 50% alum was used to treat approximately 102,000 gallons of wastewater. The average alum feed was 335mg/liter. The optimized alum feed rate was 260mg/liter. That rate for a family of 2 would require about 9-10 gallons of alum use per year. A 30 gallon slum reservoir, used in the test, would last nearly 3 years.
An interesting result about sludge formation was discovered from monitoring the sludge level on a monthly frequency. Sludge accumulation is accelerated for about 6 months after tank pumping before the anaerobic digestion can catch up to the organic input. There is also compaction of sludge with time. I observed the pump out contractors clean the tank down to bare concrete surface using a water hose to suck up the last amounts of sludge. Based on these factors, it would be beneficial to leave an inch of sludge in the tank to jump start the aerobic bacteria digestion process.
If anyone wishes to learn more, do not hesitate to contact me. 973-222-3450
On January 9, 2018 a U.S. Patent no. 9,862,625 was granted for “A system and method for treating wastewater entering a septic tank.”