Effluent Culture Research Articles

Identification of acyl-homoserine lactone signal molecules produced by Nitrosomonas europaea strain Schmidt.

Nitrosomonas europaea strain Schmidt produces at least three acyl homoserine lactone (AHL) signal molecules: C(6)-homoserine lactone (HSL), C(8)-HSL, and C(10)-HSL. These compounds were identified in extracts of chemostat culture effluent by three independent methods. The concentrations of AHL in effluent were low (0.4 to 2.2 nM) but within the range known to induce AHL-responsive systems. The absence of LuxI and LuxM homologs from the genome of N. europaea strain Schmidt suggested that AHL synthesis occurs by an alternate pathway, possibly mediated by an HdtS homolog. To the best of our knowledge, the present report is the first to document the types and levels of AHLs produced by N. europaea.

Case Report: Peritonitis by Penicillium spp. in a Patient Undergoing Continuous Ambulatory Peritoneal Dialysis

Even though prominent technical improvements in continuous ambulatory peritoneal dialysis (CAPD) treatments during the last decade, peritonitis keeps its place as an important cause of morbidity and mortality in these patients. Among them fungal peritonitis is happened to be the most difficult one to deal with and comes out serious clinical presentation. It is presented here a case of CAPD related fungal peritonitis caused by Penicillium spp. This case experienced recently relapsing bacterial episodes of peritonitis and received long term antibiotics intraperitoneally and systemically. Eventually, Penicillium spp. was detected in several cultures of peritoneal effluent and also tip of Tenckhoff catheter, therefore it was considered as a causative agent. Then, the catheter was removed and amphotericin B therapy was performed. But the general condition of the patient did not improve till surgically drainage of peritoneal collection which was determined by MR (Magnetic Resonance) examination of abdomen after antifungal treatment was completed and Penicillium spp. in the drainage samples was not determined anymore.

Is Ventilator-Associated Pneumonia in Trauma Patients an Epiphenomenon or a Cause of Death?

Ventilator-associated pneumonia (VAP) is a common infection among patients in trauma intensive care units (ICUs). It has been suggested by different investigators that VAP is an indicator of injury severity and not necessarily associated with mortality. Crude mortality rates approximating 20% have been reported for trauma patients with VAP. Most studies have involved the most severely injured patients, making it difficult to determine the relative contribution of either VAP or injury severity to death. If VAP is independently associated with mortality, this relationship should be most evident in less severely injured patients. We studied patients with less severe injuries (Injury Severity Score, ISS < 25) to determine the impact of VAP on outcomes. Patients admitted to the trauma ICU with ISS < 25 were identified from the trauma registry of a level I trauma center. Patients with penetrating injuries and those who died within 48 h of injury were excluded. Pneumonia was diagnosed using quantitative cultures of bronchoalveolar lavage effluent (>/= 10(5) colony forming units/mL). Risk factors for VAP, including age, transfusions with 24 h of admission, brain injury, and chest injury severity were analyzed. Logistic regression analysis was then performed to determine independent factors for death.Results: There were 15,492 blunt admissions over a 5.5 year study period who survived >48 h. Of these, 5,860 (38%) were admitted to the ICU, and 4,111 (70% of ICU admissions) had ISS < 25. The incidence of VAP in this group was 8%. Patients with VAP were older (47 vs 39 years), had more transfusions within 24 h (2.5 vs 0.9 units of red blood cell concentrates) and had greater injury severity by ISS (16.7 vs 12.6 points), GCS (Glasgow Coma Scale) score (11.8 vs. 13.7 points) and chest AIS (Abbreviated Injury Scale) (1.7 vs 0.9 points; all p < 0.001). Overall mortality was 4%. Mortality was 16% in patients with VAP compared to 3% in those without VAP (p < 0.0001). Logistic regression analysis identified transfusions, age, and VAP as independent predictors of mortality. Other descriptors of injury severity (ISS, GCS, or chest AIS) were not associated with death. There were 15,492 blunt admissions over a 5.5 year study period who survived . 48 h. Of these, 5,860 (38%) were admitted to the ICU, and 4,111 (70% of ICU admissions) had ISS , 25. The incidence of VAP in this group was 8%. Patients with VAP were older (47 vs 39 years), had more transfusions within 24 h (2.5 vs 0.9 units of red blood cell concentrates) and had greater injury severity by ISS (16.7 vs 12.6 points), GCS (Glasgow Coma Scale) score (11.8 vs. 13.7 points) and chest AIS (Abbreviated Injury Scale) (1.7 vs 0.9 points; all p , 0.001). Overall mortality was 4%. Mortality was 16% in patients with VAP compared to 3% in those without VAP (p , 0.0001). Logistic regression analysis identified transfusions, age, and VAP as independent predictors of mortality. Other descriptors of injury severity (ISS, GCS, or chest AIS) were not associated with death. Ventilator-associated pneumonia is independently associated with death in less severely injured trauma patients. This demonstrates the need for effective diagnostic techniques so that adequate therapy may be initiated. Prevention of VAP in less severely injured trauma patients should increase survival.

The appropriate diagnostic threshold for ventilator-associated pneumonia using quantitative cultures.

The use of quantitative cultures of the bronchoalveolar lavage (BAL) effluent to distinguish between posttraumatic inflammatory response and ventilator-associated pneumonia (VAP) is becoming more common. However, the diagnostic threshold of either 10 or 10 colonies/mL remains debatable. Because mortality from VAP is related to treatment delay, some have chosen a lower diagnostic threshold (>10 colonies/mL). This may result in unnecessary antibiotic use with its sequelae: increased resistant organisms, antibiotic-related complications, and increased costs. The purpose of this study is to determine the optimal diagnostic threshold for VAP diagnosis using quantitative cultures of the BAL effluent. Data on patients with fiberoptic bronchoscopy with BAL are maintained in a prospectively collected database at our Level I trauma center. This database was reviewed for timing and frequency of BAL and the colony counts of each organism identified. Indication for bronchoscopy was clinical evidence of VAP. VAP was defined as >10 colonies/mL in the BAL effluent. A false-negative BAL was defined as any patient who had <10 colonies/mL and developed VAP with the same organism up to 7 days after the previous culture. Over a 46-month period, 526 patients underwent 1,372 fiberoptic bronchoscopy procedures with BAL. Of these, 72% were male patients, 91% followed blunt injury, and mean age and Injury Severity Score were 43 years and 30, respectively. Overall mortality was 14%. There were 1,898 organisms identified (42% were gram-positive and 58% were gram-negative). VAP was diagnosed in 38% of BAL. Overall, there were 43 episodes in 38 patients defined as false-negative (3%). The false-negative rate was 9% in patients with 10 organisms. The most common false-negative organisms were Pseudomonas and Acinetobacter species. The VAP diagnostic threshold for quantitative BAL in trauma patients should be >10 colonies/mL. One may consider a threshold of >10 colonies/mL in severely injured patients with Pseudomonas or Acinetobacter species.

Ex-situ bioremediation of shrimp culture effluent using constructed microbial mats

In coastal countries, marine shrimp industry poses a problem with respect to the waste effluent disposal into the ocean as well as the nearby area. Constructed microbial mats offer an interesting alternative for shrimp culture effluents. The treatment concept relies on the immobilization of natural marine microbial consortium on glass wool to mitigate the levels of dissolved nitrogen from a shrimp culture effluent. Our results indicate that average efficiencies of ammonia nitrogen removal from shrimp (Litopenaeus vannamei) effluent was 97% and 95% for nitrate nitrogen, over a 20 days period of treatment. This treatment via constructed microbial mats is a technically feasible method for simultaneously reducing effluent nutrient loading (especially nitrate and ammonia) and for reducing organic loading (especially BOD5) of shrimp culture effluents.

Biotransformation of 2,4,6-trinitrotoluene in a continuous-flow Anabaena sp. system

Reductive transformation of 2,4,6-trinitrotoluene (TNT) was observed in a continuous-flow system of Anabaena sp. operated for 33 d with a 5.7 d hydraulic retention time and a range of influent TNT concentrations of 1–58 mg/l. The TNT removal efficiency of the continuous-flow system at the highest influent TNT concentration of 58 mg/l was 96.7±1.7% (mean±95% confidence interval). Culture chlorosis and growth inhibition were not observed during this study. The pseudo-first order TNT transformation rate constant values corresponding to the system performance range (0.14–0.46/h) were lower than the values previously recorded for batch Anabaena sp. cultures with less than 10 mg/l initial TNT concentrations, possibly due to an inhibition of the TNT transformation process by either TNT and/or TNT transformation products. Heterotrophic bacterial populations developed in the continuous-flow Anabaena sp. cultures also transformed TNT, but at a much lower rate than the Anabaena sp. Less than 1% of the overall TNT transformation observed in the continuous-flow system was attributed to the heterotrophic bacterial populations. The only TNT reduction products identified in both the culture media and in biomass extracts were azoxytetranitrotoluene isomers and low levels of aminodinitrotoluene isomers. TNT and TNT transformation products identified in the culture effluent and the biomass extract accounted for only about 24% of the TNT added to the system (on a molar basis). Production of soluble, polar metabolites, uptake, partial mineralization and/or sequestration of TNT and its transformation products by Anabaena may be responsible for the relatively low contaminant recovery and mass balance observed in this study.

MOLECULAR FINGERPRINTING OF MICROBIAL POPULATIONS IN SOILLESS CULTURE SYSTEMS

The molecular fingerprinting technique (PCR-DGGE) of microbial populations was successfully adopted for soilless culture systems. Relatively low concentrations of micro-organisms in the nutrient solutions could be assessed. PCR-DGGE was applied in several experiments to compare the composition and diversity of the bacterial populations in different treatments, as well as at different locations and ages of the crop. Although numbers of culturable aerobic bacteria were similar in different rockwool treatments, the PCR-DGGE patterns showed that the bacterial composition and diversity differed. The bacterial composition in treatments which were suppressive to Pythium aphanidermatum (i.e. previously used rockwool and used rockwool that was recolonised after autoclaving) differed from that in autoclaved used rockwool with a high disease incidence. Additionally, a shift in the bacterial populations during plant growth was seen. Samples of the nutrient solution from different locations in a closed soilless culture system, i.e. drain, effluent, and solution in the rockwool slabs, showed different banding patterns. The results summarised in this paper showed that PCR-DGGE is a powerful tool to study the microflora under different conditions.

Identification of Early Predictors for Post-Traumatic Pneumonia

We demonstrated that the standard clinical criteria of fever, leukocytosis, purulent sputum, and infiltrate on chest radiograph are nonspecific for the diagnosis of post-traumatic pneumonia, and only approximately 50 per cent of patients with these conditions have pneumonia. Quantitative cultures of bronchoalveolar lavage effluent will differentiate pneumonia (requiring antibiotic therapy) from systemic inflammatory response syndrome (not requiring antibiotics). Early identification of patients at risk for pneumonia can target populations for clinical research. Because risk factors for pneumonia when diagnosed by quantitative cultures have not been defined we reviewed our recent experience to identify variables predictive of pneumonia. Patients over a 22-month period who survived > 48 hours were identified from the trauma registry. Pneumonia was defined as growth of > or = 10(5) organisms per milliliter in the bronchoalveolar lavage effluent. Risk factors evaluated included injury severity and severity of shock. There were 7503 patients (75% with blunt and 25% with penetrating injuries). The incidence of pneumonia was 6 per cent (7% of patients with blunt and 2% of patients with penetrating injuries). Logistic regression analysis identified age; Glasgow Coma Scale score; Injury Severity Score; transfusion requirements during resuscitation; spinal cord injury; chest injury severity; and emergent femur fixation, craniotomy, and laparotomy as being independent predictors of pneumonia. We conclude that multiple risk factors, which are all able to be determined early after injury, are predictive of post-traumatic pneumonia. Prompt identification of this high-risk group of patients allows prognostic considerations relative to patient management schemes and targets populations for prophylactic measures or immunomodulation.

Algae in the Assessment of Industrial Wastewater Holding Ponds

The ecology and photosynthetic behaviour of the microalgalcommunity in an oil refinery wastewater holding pond was studiedwith a view to assess the role of algae in industrial effluenttreatment ponds. The biological and physico-chemical parameterswere measured for one year from February 1994 to February 1995.The assessment of algal population based on chlorophyll andprimary productivity revealed that the pond is a eutrophic systemsupporting continuous algal bloom. There was no significantcorrelation between the algal biomass and the nutrient parameterstested. A comparison of the algal gross primary production andthe community respiration for the period was done to assess thedegree of waste stabilisation, and it was found that the pondwater is of eutrophic potential. Bioassays of the effluent usingpure cultures of algae, Chlorella pyrenoidosa, Oocystispusilla and Oscillatoria quadripunctulata again confirmedthat the effluent is stimulatory to algal growth. Thus thestudy of algal community in the field surveys and the algalbioassays of the effluent, established that algae can be used asan effective tool to assess the degree of stabilisation of industrial effluents.

Hydrogen Peroxide Concentrations in Hatchery Culture Units and Effluent during and after Treatment

Abstract A raceway in a fish hatchery was treated with hydrogen peroxide (H2O2), as 1-h flow-through treatments, to simulate the New York State maximum allowable concentration (11.5 mg/L) in the receiving stream. Hydrogen peroxide concentrations were measured at various locations in the hatchery and in the receiving stream over a 96-h period. At the discharge pipe opening in the receiving stream, maximum mean H2O2 concentration was 9 mg/L at the end of the 1-h treatments and 2 mg/L 1 h later; at a point 15 m downstream (midstream) from the discharge pipe, maximum mean H2O2 concentrations were 2 mg/L at discharge and 1 mg/L or less (method detection limit) 1 h later. In a second set of experiments, a desired 100 mg H2O2/L was achieved in 1-h flow-through treatments only when the test tank was pretreated to initially establish an H2O2 concentration of 100 mg/L before initiating the flow-through treatment. When the 1-h flow-through treatment was administered without pretreatment of the test tank, a maximum H...

Growing Giant Clam (Tridacna Derasa) in Aquaculture Effluent

Juvenile giant clams (Hippopus spp. and Tridacna spp.) are highly valuable and popular in the aquarium trade due to their brightly colored mantles with various patterns. Giant clams are unique bivalves in that they possess symbiotic zooxanthellae (Symbiodinium). A previous study by the authors demonstrated the feasibility of culturing giant clams in aquaculture effluent. Among the four species tested (Tridacna derasa, T. gigas, T. maxima, and T. squamosa), T. derasa was the most suitable for culturing in effluent. The present study compared the growth, survivorship, and condition indexes of T. derasa (mean initial shell length about 83 mm) cultured in fish culture effluent or seawater for six months. The clams grew significantly faster (1.29 vs. 0.93 mm shell length/month) and had marginally significant (p = 0.076) higher survivorship (94.1% vs. 77.7%) than those in control seawater. Total (shell and tissue) and tissue weight indexes (g/mm shell length), and mitotic index (% dividing zooxanthellae) were similar between the treatment and control clams; whereas zooxanthellae density (number of zooxanthellae/g clam tissue) of the clams in the effluent tanks was 2.5 times higher than that in control tanks.

Postoperative Pneumonia

Despite the advances made in surgical critical care, the diagnosis of one of the most common infections seen in critically ill patients remains a challenge. Ventilator-associated pneumonia is associated with a 20 to 25 per cent mortality rate. There are numerous risk factors for ventilator-associated pneumonia, including underlying disease, prolonged mechanical ventilation, direct lung injury, and shock. The standard clinical criteria for pneumonia are inaccurate. Quantitative cultures of bronchoalveolar lavage effluent are accurate for the diagnosis, and it is safe to base antibiotic therapy on the results of the quantitative cultures.

Serum and effluent chloramphenicol concentrations to aid treatment of vancomycin-resistant enterococcus peritonitis

<h2>Abstract</h2> Emergence of vancomycin-resistant <i>Enterococcus</i> (VRE) has limited the antibiotic choices for treatment of gram-positive peritonitis in patients receiving continuous peritoneal dialysis (CPD). We report the case of an 83-year-old woman with end-stage renal disease receiving CPD who was hospitalized with recurrent peritonitis. Peritoneal effluent cultures showed <i>Enterococcus faecium</i> resistant to aminoglycosides and vancomycin but sensitive to chloramphenicol using the disk dilution method. Chloramphenicol 500 mg intravenously every 6 hours was prescribed, with serum and peritoneal effluent trough concentrations of 9.8 and 6.6 μg/mL, respectively. Although the recommended trough range for chloramphenicol is 5 to 10 μg/mL, the dose was increased to 1 g intravenously every 6 hours because the effluent remained cloudy. Despite this, positive peritoneal VRE cultures continued. The Tenchkoff catheter was removed with the patient maintained on hemodialysis. Four days after catheter removal, the patient died. Autopsy showed acute pericarditis with bilateral hydrothorax and pneumonia but no peritoneal inflammation indicating the peritonitis had resolved. Our case suggests that VRE peritonitis can be treated successfully with chloramphenicol and catheter removal with use of trough concentrations to guide therapy.

Impacts of Trout Culture Effluent on Water Quality and Biotic Communities in Virginia Headwater Streams

Abstract Five Virginia trout farms were selected for examination of effluent impacts on downstream water quality, periphyton production, and composition of macroinvertebrate and fish communities during fall 1994 and summer 1995. Annual trout production and feeding rates varied from 18.5 to 59.5 thousand kilograms and 15.6 to 87.6 thousand kilograms, respectively, and were correlated with discharge. Substrate embeddedness increased significantly (P < 0.07) downstream at two farms, but settleable solid concentrations in effluent were always less than 0.1 mL/L. Total ammonia nitrogen, un-ionized ammonia nitrogen, and nitrite nitrogen levels increased significantly (P < 0.001) downstream but were well below recommended thresholds for lethal exposure for aquatic organisms. Dissolved oxygen levels were significantly reduced (P < 0.001) downstream at postfeeding and predawn hours but were typically greater than 7.0 mg/L. Effluent water temperatures, pH, nitrate nitrogen, and total phosphorus concentrations did n...

Utility of Gram's stain and efficacy of quantitative cultures for posttraumatic pneumonia: a prospective study.

This prospective trial examined the efficacy of using bronchoalveolar lavage (BAL) for the diagnosis of pneumonia (PN) and the utility of Gram's stain (GS) for dictating empiric therapy. Posttraumatic nosocomial PN remains a significant cause of morbidity and mortality. However, its diagnosis is elusive, especially in multiply injured patients. The systemic inflammatory response syndrome of fever, leukocytosis, and a hyperdynamic state is common in trauma patients, especially patients with pulmonary contusion. Bronchoscopy with BAL with quantitative cultures of the lavage effluent may distinguish between PN and systemic inflammatory response syndrome, and GS of the lavage effluent may guide empiric therapy before quantitative culture results. Mechanically ventilated trauma patients with a clinical diagnosis of PN (fever, leukocytosis, purulent sputum, and new or changing infiltrate on chest radiograph) underwent bronchoscopy with BAL. Effluent was sent for GS and quantitative cultures. The diagnostic threshold for PN was > or =10(5) colony-forming units (CFU)/mL, and antibiotics were continued. Antibiotics were stopped for < 10(5) CFU/mL and the diagnosis of systemic inflammatory response syndrome was made. Causative organisms for PN were compared to GS. Over a 2-year period, 232 patients underwent 443 bronchoscopies with BAL (71% men, 29% women; mean age, 41). The mean injury severity score was 30. Sixty percent of the patients had pulmonary contusion, and 59% were cigarette smokers. The overall incidence of PN was 39% and was no different regardless of the number of BALs a patient had. The false-negative rate of BAL was 7%. GS identified gram-positive organisms in 80% of patients with gram-positive PN and 40% of patients with gram-negative PN. GS identified gram-negative organisms in 52% of patients with gram-positive PN and 77% with gram-negative PN. The duration of the intensive care unit stay relative to the timing of BAL was beneficial for guiding empiric therapy. BAL in week 1 primarily identified Haemophilus influenzae and gram-positive organisms; Acinetobacter sp. and Pseudomonas sp. were more common after week 1. Bronchoscopy with BAL is an effective method to diagnose PN and avoids prolonged, unnecessary antibiotic therapy. Empiric therapy should be adjusted to the duration of the intensive care unit stay because the causative bacteria flora changes over time. GS of BAL effluent correlates poorly with quantitative cultures and is not reliable for dictating empiric therapy.

Protected Bronchoalveolar Lavage for the Diagnosis of HIV-Associated Pneumonia

Abstract: The aim of protected bronchoalveolar lavage (PBAL) is to improve the diagnostic yield in bacterial pneumonia by combining the high sensitivity of bronchoalveolar lavage (BAL) with the specificity of the protected specimen brush (PSB). We evaluated PBAL and PSB in patients infected with human immunodeficiency virus (HIV) known to have a high incidence of bacterial pneumonia and colonization of the tracheohronchial tree. Sixty-three consecutive episodes with symptoms suggestive of pneumonia were investigated prospeetively. A comprehensive microbiologic workup was performed, including quantitative cultures for bacterial agents. Each episode was classified as “pneumonia,” “control,” or “non-infectious infiltrates.” Fifty-one episodes were identified as pneumonia. A definite microbial etiology could be established in 34/51 (67% cases, including a bacterial etiology in 15/51 (29%). The sensitivity for definite and probable bacterial pneumonia was 13/22 (59%) for PSB and 15/22 (68%) for PBAL (p value not significant). Specificity was 8/8 (100%), but there were 4 false-positive results in cultures of PSB and in cultures of PBAL effluent in patients with infiltrates on chest radio-graphs. PBAL effluent had a significantly higher mean bacterial index and specific bacterial index than PSB (5.4 ± 4.9 vs. 3.3 ± 3.2, p < 0.01, and 5.6 ± 0.8 vs. 3.8 ± 2.1. p < 0.001). The yield for Pneumocystis carinii was 13/15 (87%). PBAL, as compared to PSB, had a similar diagnostic yield for bacterial pneumonia. Both techniques were highly specific, but the specificity may be lower in patients with abnormal chest radiographs. PBAL most accurately reflected the bacterial load of the area investigated, and also conserved the yield of BAL reported for P. carinii. PBAL is a rational technique for the diagnosis of pneumonia in patients with HIV.

Comparison of mutant and parent strains of Clostridium acetobutylicum: butyrate uptake at different temperatures

A high butanol producing mutant strain of Clostridium acetobutylicum ATCC 4259 was obtained by chemical mutagenesis. Both mutant and parent strains were evaluated for butyrate uptake using the culture effluents of solventogenic fermentor-2 of the two-fermentor continuous system. Batch incubation of fermentor-2 culture effluents at 37 °C indicated lower butyrate uptake rates for mutant and parent strain, at 0.05 and 0.03 g l−1 h−1, respectively. Increased butyrate uptake rates of 0.33 and 0.26 g l−1 h−1 for mutant and parent strain, respectively, were observed when effluents were batch incubated at lower temperature of 30 °C. Butyrate conversion efficiency, at 5 ± 0.1 g l−1 of externally added butyrate, were 98.8% and 96.9% for mutant and parent strain, respectively. Butyrate up to the externally added concentration of 11.4 g l−1 did not inhibit butyrate uptake. The maximum butyrate consumption at a slightly reduced uptake rate was seen at 10.2 g l−1 butyrate concentration at 27 °C. Based on the results under different temperatures, the electron flow pattern has been computed and the mechanism for butyrate uptake has been hypothesized.

Trichosporon beigelii peritonitis in a child during treatment by continuous ambulatory peritoneal dialysis

We report a case of peritonitis caused by Trichosporon beigelii in a 2-year-old child during treatment by continuous ambulatory peritoneal dialysis (CAPD). Diagnosis was established by direct examination and culture of dialysis effluent. Infections caused by Trichosporon beigelii in children are commented.

Anaerobic treatment of intensive fish culture effluents: volatile fatty acid mediated denitrification

Denitrifying activity was examined in a laboratory-scale fluidized bed reactor coupled to a digestion basin in which fish feed was anaerobically degraded. Under these conditions volatile fatty acids (VFA; acetate, propionate and butyrate), released during anaerobic feed degradation, were found to fuel the denitrifying activity in the fluidized bed reactor. VFA fatty acid-dependent denitrification was confirmed by laboratory incubation of bacterial consortia, derived from the laboratory-scale fluidized bed reactor and a pilot-plant fluidized bed reactor. Kinetic parameters of denitrification were determined as well as the stoichiometry of VFA uptake and nitrate reduction by these denitrifying consortia. It was concluded that in closed fish culture systems, where nitrate accumulates as a result of nitrification, complete nitrate removal is possible by a combination of denitrification and anaerobic degradation of endogenous organic matter.

Anaerobic treatment of intensive fish culture effluents: digestion of fish feed and release of volatile fatty acids

Removal of organic matter and nitrate was studied in a laboratory-scale treatment system consisting of a digestion basin and a fluidized bed reactor. Fish feed was anaerobically degraded in the digestion basin and supernatant from the digestion basin, rich in dissolved organic degradation products, was used to fuel nitrate removal by denitrifying organisms in the fluidized bed reactor. Anaerobic digestion of the feed was determined in-situ using nylon-mesh bags. Feed degradation was described by considering the feed to consist of two fractions: a labile, rapidly degradable fraction and a recalcitrant, slowly degradable fraction. By using first-order kinetics, the degradation rate constants of each of these fractions were obtained allowing a quantitative prediction of sludge accumulation in the digestion basin. It was predicted that degradation rates and accumulation rates of sludge reached equilibrium after approximately 400 days of operation. The amount of sludge at equilibrium was approximately 23 times the weight of the feed which was added daily. The release of volatile fatty acids during fermentation of fish feed and sludge was determined as it is these organic compounds that mediate the denitrifying activity in the fluidized bed reactor. Predicted values for sludge accumulation and volatile fatty acid release were in agreement with measured values.