The following is a final report for the 120-day ACCELL trial from March 22 through July 20 of 2006. The major focus of the trial was the reduction of sludge hauling costs, with other peripheral benefits being improved operations, effluent quality and possible reduced aeration costs. 


Operating data for the Saputo WWTP Hinesburg facility shows a significant increase in flow and loading for 2006 versus the previous year, thus creating additional burden on the facility, and therefore, greater sludge volume. Effluent quality remained consistently good throughout the trial period in spite of the increased burden on the facility. Due to considerable change in the operating conditions of the treatment facility this year, we had to equalize the sludge data so that the data would be meaningful. Basically, we incorporated a mass balance to be able to compare “apples to apples”. The ACCELL trial demonstrated a significant reduction in sludge disposal costs when compared to like time periods for previous years on an equalized basis. The fully allocated differential for the trial period in 2006 versus 2005 shows the potential to save about $380.00/day for a 4:9:1 payback on the cost of ACCELL. When compared to the previous June/July period for 2003-2005 versus the same time frame in 2006, adjusting for flow and loading alone, the savings were $177.21/day for a payback of 2:25:1. Effluent phosphorus levels were controlled quite well during the trial period, but it was difficult to determine the degree to which ACCELL or alum contribute to this success. Additional evaluation should continue by conducting dose/response to determine the lowest level of alum required in conjunction with ACCELL to control phosphorus. Reducing the alum feed will provide further reductions in sludge disposal costs. 


Measuring improvements in an industrial or food processing wastewater treatment facility, such as Saputo, can be somewhat difficult compared to a municipal wastewater facility due to the variation in flows and loading received into the facility. This is especially true when significant increases in production occur. Therefore, creating a baseline or relevant milestone by which progress is measured can be difficult. In the case of the Saputo facility, for example, the flow (and therefore the loading) passing through the plant increased 32.25% for the time period March through June 2006 versus the same time period of 2005. Likewise, the amount of milk processed for the same time periods also increased by 25.23%, confirming the significant increase in cheese production, and therefore, the increased pressure on the wastewater treatment facility. Three factors need to be considered in evaluating the sludge reduction data for the Saputo facility: 

  • Variation of the incoming flow and loading.
  • Shifts in the Mixed Liquor Suspended Solids (MLSS), and
  • Shifts in the amount of alum used to control effluent phosphorus levels.

The Saputo wastewater treatment facility experienced a significantly greater influent flow (< 30%) for January  through June of this year vis-à-vis the same time period of 2005. Likewise, the amount of milk being processed has also increased by over 25%. These factors combine to place a greater burden on the facility and will, under normal circumstances, produce a concomitant increase in sludge production. This increase in load received by the wastewater treatment facility can manifest itself in many other ways, including lower terminal dissolved oxygen, and poorer effluent quality, particularly if the treatment facility is nearing its design capacity. The next point for consideration is the control of biological solids, or MLSS, in the treatment facility. Under ideal conditions, the operator will normally attempt to operate the facility at a uniform level. Because the Saputo facility does experience high organic loads and large variations in the incoming load, the plant normally operates a MLSS level of approximately 8500 mg/L. Since the use of ACCELL reduced the production of biological solids, the MLSS levels will decrease unless the amount of sludge being wasted is reduced. A drop of 500 mg/L in the MLSS means that an extra 2.1 try tons was wasted, that should have been retained in the treatment process. Eventually, the operator must reduce the amount of sludge being wasted to regain an operating balance in the facility. The last factor must be considered in measuring sludge production of sludge hauling costs, that is, the amount of alum being used to reduce the phosphorus levels in the wastewater effluent. The alum being used is a 50% solution with a specific gravity of approximately 1.45. This yields a weight of 12.1 pounds per gallon, or about 6 pounds of alum that is contributing to the total sludge being hauled from the facility. Therefore, for every gallon of alum that is added to the wastewater to treat the phosphorus, $2.69 is added to sludge hauling costs. In calculating some of the sludge-hauling numbers for 2005 and 2006, we have calculated the differential in those numbers since heavier use of alum has been used since January to meet State of Vermont goals for phosphorus discharge in the wastewater effluent. The “Proposal” for the ACCELL trial issued on February 23rd stated the following: “The primary objecting would be to reduce the amount of sludge being hauled from the facility. The time required to acclimate the biology in the facility runs between one and two sludge ages, or approximately 30-60 days. At that point, we should be achieving the optimal sludge reduction. Therefore, we would determine the sludge reduction based on the 61-120 day period of the 120-day trial. “We suggest that we use the average tons of sludge hauled for the first two quarters for the years 2003-2005 as a guideline for evaluating the effectiveness of ACCELL. While this is not perfect because wasting is normally higher as you move into the warmer season, this seems to be the most practical approach short of running the  trial for a year or more.” 

Trial Results: 

Sludge reduction was evaluated using two different baselines. The first method for determining the sludge reduction savings was calculated for the 61st day through the 120th day of the trials, or May 21st through July 20th, comparing 2006 versus 2005. In this case, we were able to incorporate the shift in MLSS and the additional burden from the higher alum feed rates for the 2006 because of available data. The second was comparing June and July of 2006 versus those same two months for the three-year period of 2003-2005. Since we only had data through July 27th of 2006, the data is compared on a dry ton per day basis. This data is adjusted for the differential in the load/flow for June/July 2005 versus 2006. We did not have the required information available to analyze the effects of changes in MLSS or alum usage, which would also affect the sludge results. It should also be noted that three rather significant “spills” occurred in July of 2006, but the degree to which these may have contributed to an increase in the load to the treatment facility, ergo, more sludge, is unknown. These spills occurred on July 1st, 11th, and 14th. Some of this material may have been diverted to the spill tank, but precise values have not been determined. It should be noted, however, that the dissolved oxygen, which had been running at approximately 2.5 mg/L prior to July 1st of this year, dropped dramatically on July 1st to about 0.69 mg/L, indicating a significant increase in the influent loading. These spills, in conjunction with the high lagoon temperatures (33° - 34° C) also contribute to the low dissolved oxygen levels. The May 21 through July 20, 2005 versus 2006 data is as follows: The first set of charts shows the comparison of the raw sludge hauling data for the two time periods, the flow-compensating factor for the increased flow/load, and the adjusted sludge hauling data. 

Raw Sludge Hauled Data 

Dry Tons: May21-June 2022.70020.573
Dry Tons: June 21-June 2017.06920.181
Total Dry Tons39.76940.754
Dry Tons/Day0.6630.679


 Wastewater Influent Flow / Factor Calculation 

Avg. MGD Flow: May 21-June 2022.70020.573
Ag. MGD Flow: June 21-June 2017.06920.181
Total 39.76940.754
Daily Avg.0.6630.679


Divide 2006 Avg. Flow0.1608
Daily 2005 Avg. Flow0.1245


Sludge Reduction – Flow Adjusted 

Dry Tons / Day0.6630.679
Factor 1.292
Adjusted Dry Tons/Day 0.8570.679


The sludge hauling figures when compensating for the significant differential of wastewater flow and loading into the treatment plant, shows a reduction of 0.178 dry tons per day of sludge being hauled. The cost of sludge disposal is currently set eat $859.00/dry ton, reflecting a savings of $159.31/day. The cost of feeding ACCELL is $78.75/day, resulting a total net savings of $80.56/day, with a payback of 2.02:1. However, the MLSS in the lagoons dropped from 7500mg/L to 6000mg/L between May 21st and July 20th of this year. Based on a total capacity of 1,000,,000 gallons for the lagoons, this means that a total of 12,750 pounds of sludge (or 6.375 dry tons) was  wasted that should have been retained in order to maintain an equilibrium MLSS value of 7500. It should be noted that throughout the trial period, the MLSS values were declining and maintaining equilibrium MLSS value of 8500 mg/L is the goal. To understand the true value of ACCELL, we must also compensate for the excess wasting during this time period. 

These figures are as follows: 

Total Dry Tons51.4240.74
MLSS Adjustment
Total 51.4234.365
Adjusted Dry Tons/Day0.8570.572

The sludge hauling costs, when adjusted for changes in both increased flow/loading and MLSS levels in the lagoons, show a reduction of 0.285 dry tons/day. This translates to a savings of $255.08/day, or a net savings of $176.33/day with a payback of 3.24:1. Incorporating the third factor, alum usage for phosphorus control, results in an even more favorable conclusion. Phosphorus levels in wastewater effluent have become a major issue with the state and federal EPA agencies, with new and stricter regulations currently being introduced. Since January of 2006, Saputo has undertaken the task of reducing and better controlling the levels of phosphorus in their effluent. This is being achieved by increasing the amount of alum in the treatment process. Unfortunately, increased alum usage translates directly into increased sludge. Comparing the May 21st through July 20th time periods for 2005 and 2006, we find that alum usage had increased from approx. 4190 gallons in 2005, to 5056 gallons in 2006. Based on 6 pounds of alum per gallon of solution, the increase in alum consumption was contributing a total of 16,738 more pounds, or 8.369 dry tons to the sludge composition in 2006 versus that of 2005. Using the figures from the flow/loading and MLSS adjustment data, the alum differential appears as follows: 

Total Dry Tons51.4234.365
MLSS Adjustment
Total 51.4225.996
Adjusted Dry Tons/Day0.8570.433

The composite adjusted average daily sludge disposal for June and July of 2003 through 2005 is 0.835 dry tons per day. This does not take into account any possible effects from variations in the MLSS levels or alum feed rates. This rate when compared to the average daily flow for June/July of 2006 of 0.637 dry tons/day shows a reduction of 0.198 dry tons/day. The cost of sludge disposal is currently set at $895.00/dry ton, reflecting a savings of $177.21/day. The daily cost of feeding ACCELL is $78.75/day, resulting a total net savings of $98.46/day, with a payback of 2.25:1. 

Additional results: 

We also reviewed the effluent data for 2005 versus 2006, and found that, overall, slight improvements were seen in the effluent quality. It should be that the effluent quality was quite good to begin with: a reflection of the operation of the facility by its personnel. We also believe that the potential for poorer effluent quality was present due to the increased pressure from the increased flow and loading in the influent. We also were interested in observing the dissolved oxygen levels, considering the possibility of reducing aeration costs. However, due to the way the aeration system is set up, the high operating MLSS levels, and the tremendous swings in Loads, we feel that it is prudent to continue to operate the aeration in the current manner. For example, dissolved oxygen levels in both lagoons dropped in July, and can be correlated with the timing of the three spills. Further, the lagoon temperatures of the lagoons were operating 3-4° C higher than seen in 2005, thus exacerbating the D.O. issue. However, effluent D.O. levels remained good. Effluent phosphorus levels were well controlled during the ACCELL trial, however, increased alum feeds were also used at this time. The following chart shows the effluent phosphorus levels versus  the gallons of alum used per day. In addition, the alum usage was not correlated with the wastewater flow and loading numbers. 

2005 Phos.-mg/LGPD/50% Alum2006 Phos.-mg/LGPD/50% Alum 
January 1.4742.5510.58123.81
July 7.2469.40