Abstract

A large pulp and paper mill in the upper Midwest was experiencing accumulation of solids in a wastewater treatment lagoon following their aeration basin and secondary clarifier. Core sampling was used to measure changes in sludge before and after the lagoon was dosed with [PRODUCT NAME]. Results included reduced sludge volume and increased hydraulic space.

Background

The buildup of sludge was leading to hydraulic short-circuiting and loss of treatment capacity in the lagoon. The cause of excessive solids loading in the lagoon was due to unsettled solids and high BOD in the secondary clarifier effluent, as well as poor facultative digestion within the lagoon. A survey conducted in 2013, by a third party indicated that the entirety of the lagoon is 238 million gallons at 8’8” deep and 43.5% filled with sludge. Surveying and samples taken by MDG on Oct 7th, 2015 illustrated that solids loading in SSE portions of the lagoon were the most dramatic.

A recommendation in fall of 2015 was made to use bioaugmentation product, [PRODUCT NAME], to enhance biological digestion of accumulated solids in the lagoon. In June of 2016, the SSE portion of the lagoon was treated with [PRODUCT NAME] in an effort to remove accumulated organic solids.

The objective of treatment was to demonstrate with quantifiable results, the digestion of accumulated solids after addition of [PRODUCT NAME] in a portion of the lagoon. Success is measured by increased hydraulic space (depth to sludge blanket) and removal of solids in the portion of the lagoon treated and monitored after 90 days.

Methods

Vertical core samples of the strata in the top 3’ of the lagoon (surface elevation 698.5’) were taken from designated location numbers 1, 2, 3 & 4 within the treated area (Figure 1). Surface area of treated section is approximately 384,250 ft2 (725’x530’). Only the top 3’ of the lagoon was sampled because greater depths could not be consistently reached due to sludge density. The volume of the 3’ strata of the lagoon monitored within the treated area is approximately 42,700 cubic yards. Core samples were taken prior to treatment with [PRODUCT NAME] and then again 90 days after to determine changes in sludge. Data recorded from core sampling included depth to sludge blanket (inches), total solids (mg/l) and % volatile solids.  

Product Application Procedure:

[PRODUCT NAME] was applied to treat the SSE portion of the lagoon directly north of activated sludge basin and west of the influent area (Figure 1) on June 20th, 2016. This section was chosen for its high sludge build-up and because it is a smaller, somewhat hydraulically short circuited from the rest of lagoon. The lagoon in this section was recorded to be approximately 9’ deep; however solids were coming very near the surface. To dose this section, 22.5 kg of [PRODUCT NAME] was diluted with water in a 55-gallon drum, mixed with an electric mixer, and allowed to rest for one hour. After resting period, solution was re-mixed and the entire solution was poured into the lagoon by pails along the west bank of the treated section. 

Core Sampling Procedure:

Prior to the collection of the baseline samples, the lagoon depth was determined by recording the level at the point of discharge. A 1.5” clear, graduated, PVC sampler equipped with a 1.5” ball value on the bottom was used for taking core samples. At each sampling location, the sampler was slowly lowered into the lagoon until it reached a level of 3’ below the lagoon surface (elev. 698.5). The ball value was then closed and the sampler removed from the lagoon. The core sample was released from the sampler into a 5-gallon bucket by opening the ball valve. Once the sample was collected in the bucket it was mixed via gentle swirling. A sub-sample of the mixture (~500 ml) was collected into a labeled plastic sample bottle and sent off to a third party laboratory for analysis of total solids (mg/l) and % volatile solids.

The core sampling process was repeated 90 days after treatment. Due to the lagoon level being approximately 0.5’ higher than it was for baseline sampling, the sampler was slowly lowered to a depth of 3.5’ below the surface before the ball value was closed. The sampler was removed from the lagoon and placed into a 5-gallon bucket. The ball value was slowly opened and only the bottom 3’ of the core sample was allowed to release into the bucket by closing the ball valve with the last 0.5’ of liquid inside the sampler. The sampler was then removed from the bucket and the remaining contents emptied back into the lagoon. Mixing, testing and subsampling of core sample was then conducted following the same procedure as before.

Results

By every measure, sludge was reduced in the treated section 90 days after application of [PRODUCT NAME]. The sludge blanket was lower, the amount of solids in the sludge blanket was reduced and the amount of organic content in the sludge was reduced. The sludge blanket within the strata lowered 8.4”. This drop in sludge blanket equates to freeing up ~9,900 cubic yards of hydraulic space (Figure 2). The concentration of solids within the monitored strata reduced 89% after treatment. This equates to ~1290 dry tons of solids being removed from the measured strata alone (Figure 4 & Table 1).

Of the 1290 dry tons of solids removed from the measured strata, 557 tons were volatile (organic) and 733 tons were inorganic (Table 1). Ninety (90) days after treatment the content of the sludge in the strata also changed. Prior to treatment, 43% of the sludge was volatile (organic), 90 days after treatment the volatile portion of the remaining sludge reduced to 41%.