COD Excess in Wastewater

Bioaugmentation at Citrus Processing Plant Improves COD Reduction and System Stability While Reducing Upsets

Background
A Florida citrus processor operates a 2 mgd (7571 m3/d) wastewater plant. From January to March, oranges are harvested, and juice production is at full scale. Historically, the wastewater plant becomes unstable during this period due to increased COD loading and load variability. The 2000 production season was particularly difficult and upsets were frequent.

In the months leading up to the 2001 production season Novozymes Biologicals, Inc. worked with the juice processor to develop a bioaugmentation program to improve stability and effluent quality at the wastewater plant. To optimize the program, Novozymes conducted a treatability study using BI-CHEM®1003FG, plant mixed liquor, raw wastewater, and varying amounts of press liquor, a highly concentrated waste by-product of citrus processing suspected of causing inhibition at 1.0% of the influent flow. The results confirmed a significant inhibitory delay in microbial growth at 1.0% press liquor, however, reactors with augmented MLSS removed 45% more sCOD (58% vs. 40%) than nonaugmented reactors over the course of the study.

Based on these results and the fact that press liquor spills are infrequent, but can lead to plant upsets, Novozymes Technical Service Engineers suggested a bioaugmentation program and a biomass pre-acclimation device (PAD) to enhance treatment performance. A PAD is an on-site, aerated reactor that uses influent wastewater to pre-acclimate BI-CHEM® cultures to the site-specific wastestream, increase the number of bacterial cells and semi-continuously release cells during log growth phase (when they are most active). A bioaugmentation program started on January 3, 2001.

Results
During the 2001 production season, the average daily influent COD load increased by 11% compared to 2000 and was more variable. Despite the higher influent loading during the 2001 season, the daily effluent COD load average was 44% lower and less varied than the previous year. Total suspended solids (TSS) removal efficiency in the 2001 season averaged 94.6%, an 8.7% increase from the previous year. During the 2001 season, TSS loading to the aeration basin averaged 12,519 lb/day (5679 kg/day), a 26.4% increase from the previous year of 9217 lb/day (4181 kg/day). Despite the increase, the average daily effluent load was 61% lower; 541 lb/day (245 kg/day) in 2001 vs. 1387 lb/day (629 kg/day) in 2000. In addition to plant operational data, system health was documented weekly through the use of microexams. Samples were sent to the Novozymes Biologicals? R&D facility for floc analysis, filament identification and microlife profiling. Throughout the trial, the floc appeared healthy and filamentous abundance was normal. Indicator organisms including swimming ciliates, stalked ciliates and rotifers were abundant during the entire production season, signifying good health.

PAD Optimization
A PAD built by Novozymes Biologicals, is more than simply a ?bug tank?. Novozymes Technical Service Engineers personally install each PAD because every application is different. To get the maximum benefit from a PAD, it must be optimized and tuned for each specific wastestream to encourage consistently high growth rates. When operated properly, the PAD not only increases the number of BI-CHEM® cells, but also further acclimates them to the specific wastewater such that when they are discharged to the plant, their rate of growth significantly exceeds that of the indigenous biomass. A PAD program by Novozymes Biologicals offers the best protection against shock loads and increases system stability. For more information, contact Novozymes Biologicals? Technical Service Department at 800-859-2972.

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