Demonstrating Compliance with Stringent Nitrogen Limits Using a Biological Nutrient Removal Process in California's Central Valley.

The Sacramento Regional County Sanitation District (District) must be compliant with stringent nitrogen limits by 2021 that the existing treatment facilities cannot meet. An 11-month pilot study was conducted to confirm that these limits could be met with an air activated sludge biological nutrient removal (BNR) process. The pilot BNR treated an average flow of 946 m(3)/d and demonstrated that it could reliably meet the ammonia limit, but that external carbon addition may be necessary to satisfy the nitrate limit. The BNR process performed well throughout the 11 months of operation with good settleability, minimal nocardioform content, and high quality secondary effluent. The BNR process was operated at a minimum pH of 6.4 with no noticeable impact to nitrification rates. Increased secondary sludge production was observed during rainfall events and is attributed to a change in wastewater influent characteristics.

Process Performance of Secondary Effluent Granular Media Filtration with and without Preozonation.

A 10-month pilot study compared the performance of conventional granular media filtration (CGMF) with granular media filtration with preozonation (OGMF) to determine the effects of preozonation on filter performance. Filtration recoveries were lower for OGMF compared to CMGF when operated at a loading rate of 18.3 m/h. Operation at 18.3 m/h met turbidity requirements for California Department of Public Health Title 22 unrestricted reclaimed water requirements for both OGMF and CGMF. Preozonated secondary effluent at a transferred dose of 3 mg/L resulted in an increase in ultraviolet transmissivity (UVT) of approximately 6% and greater than 5-log inactivation of male-specific bacteriophage MS2. Wet weather flow events resulted in UVT decrease and a decline in MS2 inactivation to less than 3 log attributed to higher ozone demand in the secondary effluent. Preozonation increased N-nitrosodimethlyamine (NDMA) concentration approximately 10 times, but subsequent filtration reduced levels to secondary effluent values. A net increase in NDMA was observed at times.

A critical review of nuisance foam formation and biological methods for foam management or elimination in nutrient removal facilities.

The classifying selector was introduced to the wastewater industry in 2001, after several successful full-scale applications. The classifying selector concept distinguishes itself from the earlier surface foam wasting schemes in that negative selection pressure is maintained so that nuisance foam-causing organisms cannot gain a foothold in sufficient numbers to cause nuisance foams. The propensity of the nuisance-causing organism to attach to bubbles and establish a rising velocity is used to enrich them in a surface mixed liquor layer, where they are wasted. Neither standard texts nor the Water Environment Federation's Manuals of Practice adequately describe this, and as a result, the benefits of foam elimination obtainable through use of the classifying selector concepts have not been broadly obtained in our industry. In certain types of processes that are inherently foam trapping situations, the only solution is surface foam wasting, as foam cannot be eliminated. Potential efficiency gains possible in these situations are addressed.

Analysis of organic nitrogen removal in municipal wastewater by reverse osmosis.

The results of a pilot study that was conducted to determine the total nitrogen removal by the reverse osmosis process are presented. The organic nitrogen removal rates are compared with removals observed from three full-scale reverse osmosis facilities and four pilot studies. The results of this analysis suggest that organic nitrogen removal is variable and that reverse osmosis may not consistently produce total nitrogen levels less than 1.0 mg/L without additional treatment. Three hypotheses to explain the variability in organic nitrogen removal in the different data sets are presented.

Petroleum refinery stripped sour water treatment using the activated sludge process.

A pilot study was performed over 91 days to determine if the activated sludge process could treat a segregated stripped sour water (SSW) stream from a petroleum refinery. The study was performed in two periods. The first period was terminated after 19 days, as a result of excessive sludge bulking. The elimination of sludge bulking during the 70-day second period is attributed to operational changes, which included aerating the influent to oxidize reduced sulfur, adjusting the influent pH, and adding micronutrients to satisfy biological requirements. The pilot plant provided a chemical oxygen demand (COD) removal of up to 93%. Nitrification was achieved, with effluent ammonia values < 1 mg-N/L. These results indicate that direct treatment of SSW with the activated sludge process is possible and has direct application to full-scale petroleum refinery wastewater plant upgrades.

Changes in mixed liquor and organic foulant properties affect membrane fouling for non-nitrifying and nitrifying biological conditions.

A submerged membrane bioreactor treated settled municipal wastewater at a non-nitrifying solids retention time (SRT) condition (2 days) and a nitrifying SRT condition (10 days), to determine the effect of nitrification on mixed liquor properties and membrane fouling. Membrane fouling rates were almost 10 times greater at the 2-day SRT compared with the 10-day SRT, and results showed increased concentrations of high-molecular-weight organic molecules at the 2-day SRT. The Fourier transform infrared spectroscopy (FTIR) results of the fouled membrane from the 2-day SRT exhibited strong peaks for carbohydrates, while the fouled membrane from the 10-day SRT did not. This is consistent with the fact that, although the total carbohydrate soluble microbial product concentration was highest at the 10-day SRT, the carbohydrate consisted of mostly low-molecular-weight (< 1 kDa) molecules, and 97% of this carbohydrate passed through the membrane at the 10-day SRT.

Analyzing wet weather flow management using state of the art tools.

Optimal secondary clarifier performance is crucial to meet treatment requirements, especially when treating peak wet weather flows (PWWFs), to prevent high effluent suspended solids (ESS) concentrations and elevated sludge blankets. A state-of-the-art computational fluid dynamic (CFD) model was successfully used as a design and diagnostic tool to optimize performance for municipal wastewater treatment plants subject to significant PWWFs. Two case studies are presented. For Case Study 1, the model was used to determine the number of secondary clarifiers that will be necessary to treat future PWWF conditions for a plant under design. For Case Study 2, the model was used to identify modifications that are currently being made to increase the clarifier capacity for handling PWWF.

Influence of mixed liquor properties and aeration intensity on membrane fouling in a submerged membrane bioreactor at high mixed liquor suspended solids concentrations.

This paper presents the results of 195 days of pilot-scale submerged membrane bioreactor (SMBR) experiments on settled municipal wastewater. Short-term and long-term thickening experiments were performed at a constant membrane flux of 30L/(m(2)h) to determine the impact of the following mixed liquor properties: colloidal material, soluble COD, soluble microbial products, extracellular polymeric substances, and viscosity along with aeration intensity on membrane fouling at high mixed liquor suspended solids (MLSS) concentrations. The normalized permeability declined with increasing MLSS concentrations in all experiments and increasing the coarse bubble aeration intensity increased the permeability at a given MLSS concentration. Using a dynamic approach, this work demonstrates the importance of mixed liquor viscosity, which impacts the efficacy of the coarse bubble aeration, in sustaining membrane permeability. Over an extended thickening time period, a small increase in MLSS concentration and mixed liquor viscosity becomes more prevalent and leads to greater permeability decline at a given MLSS concentration.

A comparison of the physical, chemical, and biological properties of sludges from a complete-mix activated sludge reactor and a submerged membrane bioreactor.

The properties of sludges from a pilot-scale submerged membrane bioreactor (SMBR) and two bench-scale complete-mix, activated sludge (CMAS) reactors treating municipal primary effluent were determined. Compared with the CMAS sludges, the SMBR sludge contained a higher amount of soluble microbial products (SMP) and colloidal material attributed to the use of a membrane for solid-liquid separation; a higher amount nocardioform bacteria, resulting from efficient foam trapping; and a lower amount of extracellular polymeric substances (EPS), possibly because there was no selective pressure for the sludge to settle. High aeration rates in both the CMAS and SMBR reactors produced sludges with higher numbers of smaller particles. Normalized capillary suction time values for the SMBR sludge were lower than for the CMAS sludges, possibly because of its lower EPS content.

Effects of sludge properties on the thickening and dewatering of waste activated sludge.

The thickening and dewatering of waste activated sludge, from a pilot-scale submerged membrane bioreactor and two bench-scale, complete-mix activated sludge reactors (high-shear and low-shear aeration) treating the same municipal primary effluent, were investigated. Solids settling and compaction were measured using the diluted sludge volume index (DSVI) analysis and a batch centrifugation analysis, respectively. Elevated levels of filamentous microorganisms resulted in higher DSVI values and lower centrifuged pellet concentration. Elevated levels of nocardioform bacteria resulted in lower solids float concentrations, and higher colloidal material reduced solids recovery in batch flotation experiments. Sludge filterability, measured as time-to-filter, was shown to be a function of extracelluar polymeric substances and colloidal material, where higher levels of either reduced sludge filterability. Additional research is necessary to confirm these results using full- or demonstration-scale thickening and dewatering units.

The effect of organic loading on process performance and membrane fouling in a submerged membrane bioreactor treating municipal wastewater.

The results of experiments on municipal wastewater primary effluent are presented for a pilot-scale submerged membrane bioreactor (SMBR). The SMBR pilot plant employed an ultrafiltration membrane with a nominal pore size of 0.035 microm and was operated at a constant membrane flux of 30 L/m(2)h. The mixed liquor suspended solids (MLSS) concentration was maintained at 8+/-2 g/L and steady-state fouling rates were determined for 10, 5, 4, 3, and 2-d MCRTs, corresponding to food-to-microorganism (F/M) ratios of 0.34, 0.55, 0.73, 0.84, and 1.41 gCOD/gVSS d, respectively. Membrane fouling rates increased as the F/M was increased. Steady-state membrane fouling rates were correlated with total soluble microbial products (SMP) concentrations. The membrane fouling rates did not correlate well with soluble COD measured on a 0.45 microm membrane filtrate of mixed liquor or with soluble COD rejection (effluent COD/soluble COD).