Hauling Less Costs Less: A Recipe for Biosolids Volume Reduction

A microbial product on a growth-promoting substrate helps a Massachusetts clean-water plant sharply reduce biosolids volume and drive down handling costs.

Hauling Less Costs Less: A Recipe for Biosolids Volume Reduction

The South Deerfield Wastewater Treatment Plant in a view looking toward the northeast side of Mount Sugarloaf. 

Biosolids production and hauling costs had tripled in recent years for the Town of Deerfield (Massachusetts) Wastewater Division. As landfills and incinerators were mothballed for various reasons, those costs were expected to escalate, and I knew I needed to do everything I could as chief operator to reduce them.

I had considered a number of products professing beneficial results in solids reduction, but I had never tried them, mainly due to reports from other operators who had done so and were disappointed. That, combined with relatively high initial cost without knowing how much I would need to use and with no guarantee of results or any proof to back up the claims, convinced me that operating the plant conventionally was my best bet.

When I saw that Aqua Assist from Drylet had won a 2017 Water Environment Federation Innovative Technology Award, my interest was piqued. I went to the website, watched the videos and learned about the line of products. Despite my skepticism, I called Drylet and explained what I was looking to do.

We began a trial on Nov. 12, 2017. By the following February, we went from sending out eight 9,000-gallon loads of biosolids per month to five loads at an average of 3 percent solids. At the end of March, we began skipping waste events altogether and started wasting only once per week. The improvements continued and are still going strong.

Proceeding to trial

Our South Deerfield Wastewater Treatment Plant is a small extended aeration facility with no headworks, one mechanical floating surface aerator and only one small circular final clarifier. We waste sludge in batches averaging 20,000 gallons. We turn off the return activated sludge pumps and let the solids build up in the clarifier for several hours, then waste to a sludge holding tank, introducing a coagulant along the way.

In investigating Drylet, I learned that they would back an entire trial with support, computer modeling, and Ph.D. experts to talk to. In addition, if I thought Drylet was not delivering on promises or claims made, I would not have to pay a dime for the trial product.

With Aqua Assist, Drylet provides a proprietary blend of microbes in a dry-to-the-touch powder with enormous surface area. The free-flowing powder delivers high-performing microbes along with a substrate on which they can readily grow, multiply, and accelerate the breakdown of organic material in the waste stream.

The company stated that the product could reduce biosolids production by as much as 50 percent. We signed on for a three-month subscription trial. Drylet provided all the product based on our plant size, flow, and configuration, along technical support and assistance.

Wasting in batches

To jump-start the population of Aqua Assist microbes in the system, we began by adding 2 pounds per day to the aeration tank at the splitter box where the influent and RAS flows meet just ahead of the aeration tank. After a couple of weeks, we reduced that to 1 pound per day. Dosage is mainly based on average flow, average influent BOD, and other variables depending on plant configuration. 

For several weeks we saw little if any change. Then, little by little, we noticed better settling, clearer effluent, and less bulking than usual. At that point we started slowly reducing our wasting, and Drylet directed us to let our mixed liquor suspended solids concentration climb much higher than I was used to.

Before using the Aqua Assist product, we ran an MLSS level of 2,800 to 3,400 mg/L during the warm season and 3,400 mg/L to 4,000 mg/L in winter, always keeping the bottom of the final clarifier scoured out. All the sludge was kept in the aeration tank where it could do the most work. 

Then Drylet asked us to let our MLSS climb to 4,000 and eventually 5,000 mg/L. At that point I was out of my comfort zone and needed assurance that this would not backfire and leave us with tons of solids carrying over the final clarifier weirs and into the chlorine contact chamber. I had visions of coming in one morning to find a 3-foot blanket of sludge floating on top of my clarifier with 100 pounds per hour of solids going out into the Connecticut River, our receiving stream.

Staying the course

I received the assurances I needed and stayed with the advice Drylet was giving weekly on how to steer the plant along operating in a new way. They asked us to keep a blanket of a couple feet of sludge in the final clarifier because that facultative environment would help with BOD removal and give the microbes more time to reduce the biosolids inventory.

The results have been highly satisfactory. In 2017 we had 86 9,000-gallon loads leave the plant at an average cost of $804 per load. That meant an average of seven loads per month, or $5,762 per month.

In May 2018, we generated four loads, or 57 percent less. At the fiscal year 2018 average of $827 per load, that translated to $2,481 saved during May alone. In June 2018, we sent out two loads at a cost of $1,654. That compares to nine loads that left the facility in June 2017. The cost difference is $5,789. Given our $500 monthly subscription to receive the Aqua Assist product and support services, the monthly net savings over June last year were $5,289.

Lessons learned

Aqua Assist allowed me latitude to operate differently and in a way that reduces our operating cost significantly. When our trial ended in February, we agreed to continue for an entire year to see what would happen during the warm seasons.

I cannot think of anything else I could do or add to our treatment process for such a small outlay that would reduce our biosolids so significantly. We found a simple solution to our escalating biosolids hauling problem that had a significant cost impact, while giving us no bulking, no rising solids in the clarifier, excellent denitrification, very low nutrient numbers, and single-digit TSS and BOD values, all without infrastructure changes or additions.

Drylet delivered its subscription model with excellent technical support from people who are helpful, knowledgeable and professional. The company asked for a couple years of data in order to configure a pilot plant. They helped steer us along toward better treatment and lower biosolids production. Weekly conference calls helped calm our nervousness about MLSS concentrations and other concerns.

Aqua Assist is working well at our old extended aeration plant, which is in need of upgrading. Even with all the rags, grit, and other trash all swirling around, the microbes are getting the job done well. 

About the author

Keith Milne is chief operator with the Town of Deerfield Wastewater Division in South Deerfield, Massachusetts. 


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