CICEET Progress Report for the period 9/15/04 Through 3/15/05

Project Title: Autotrophic Biological Denitrification with Hydrogen or Thiosulfate for Complete Removal of Nitrogen from a Septic System Wastewater
Principal Investigator(s): Sukalyan Sengupta, Sarina Ergas
Project Start Date: September 1, 2003

Figures

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Tables

Table 1

2. Evaluate the effect of change of solid-phase buffer in one bioreactor from marble chips to crushed oyster shells.

3. Evaluate the effect of addition of small amounts of domestic wastewater on denitrification rates, cell yields and system stability in autotrophic denitrification of bench-scale system (both H₂ and S⁰).

4. Evaluate the effect of dissolved oxygen on denitrification rates and cell yields in autotrophic denitrification of bench-scale systems (both H₂ and S⁰).

Tasks to meet objectives
1. Sulfur oxidizing denitrification field-scale bioreactors:
Two field-scale units have been assembled and placed on the Massachusetts Alternative Septic System Test Center (MASSTC) site. The details regarding the construction and operation of both units are available in earlier progress reports. Both units had marble chips as a solid-phase buffer until November 11, 2004. Starting November 11, 2004, one of the units was emptied and filled with a fresh batch of sulfur pellets and crushed oyster shell as a solid-phase buffer at the same 3:1 ratio by volume. The new bioreactor was seeded with sludge from the old marble-chip bioreactor that was replaced. Both the reactors have been operated under the transient flow conditions as specified in the National Sanitation Foundation (NSF 40) protocol. Both bioreactors have been monitored for pH, Total Alkalinity, Nitrate-Nitrogen, Nitrite-Nitrogen, Sulfate, Chemical Oxygen Demand, Biochemical Oxygen Demand, and Total Kjeldahl Nitrogen.

2. Sulfur oxidizing denitrification bench-scale bioreactors:
Two bench-scale upflow, packed bed bioreactors were operated for approximately 300 days. The reactors were initially packed with a mixture of sulfur pellets and marble chips, seeded with sludge from the Lakeville school wastewater treatment facility (Dartmouth MA) and operated with a synthetic nitrified wastewater with empty bed contact time (EBCT) of 16 hours. After a six-week acclimation period, the reactors were repacked with media consisting of the acclimated sulfur pellets with either crushed oyster shell or limestone (3:1 ratio by volume) to evaluate the effect of different buffering agents on biological denitrification. Concentrations of NO₃^-, SO₄^-, and NO₂^- as well as TALK and pH in the influent and the effluent were normally monitored every 48-72 hours. COD, TOC, turbidity and DO were monitored periodically. The two columns were operated side-by-side at an EBCT of 8 hours and differing buffers for approximately six months. On day 174, we stopped sparging the influent with N₂ gas to examine the effect of dissolved oxygen on denitrification. Finally, the limestone column was shut down and the influent to the oyster shell column was amended with acetate (20 mg COD/L). The oyster shell column was operated for approximately two months with the acetate-amended feed.

3. Hydrogenotrophic batch culture experiments:
Hydrogenotrophic denitrifying bacteria were cultured from wastewater obtained from the Berkshire mall (Lanesboro, MA) and Belchertown, MA wastewater treatment plant. Batch cultures were set up in 1000 mL Erlenmeyer flasks at 20 ° C with shaking. H₂ was introduced to the headspace of the flasks. Local groundwater amended with 50 mg/L NO₃^-N, 0.25 g/L NaHCO₃, and other trace nutrients required for growth was used as synthetic wastewater, which was introduced to the flasks each time the NO₃^--N concentration decreased below 1 mg/L.

4. Bench-scale hollow fiber membrane bioreactor construction:
A laboratory-scale HFMB system was constructed of glass tubing enclosed by anodized aluminum end plates sealed with Viton O-rings. Its overall length is 76 cm and the total volume is 500 mL. The membrane bundle used for H₂ transfer is composed of polyolefin multilayer hollow fibers (Mitsubishi MHF200TL) and was manufactured by Porous Media Inc. (St. Paul, MN). The bundle contains 200 fibers with an active length of 50 cm. The inner diameter of the membranes is 200 mm, the outer diameter is 284 mm, the porosity is 42% and the membrane occupies 1.3% of the total reactor volume. Nitrate contaminated synthetic wastewater containing 50 mg NO₃^--N/L is provided to the shell side of the reactor using a chemical feed pump.

5. Hydrogen membrane mass transfer tests:
Hydrogen mass transfer coefficients were determined by operating the reactor at varying H₂ partial pressures and liquid recirculation rates. Influent and effluent gas and liquid phase H₂ concentrations were measured over time using a Hewlett Packard 5890 GC equipped with a packed column and thermal conductivity detector.

6. Hydrogenotrophic hollow fiber membrane bioreactor (HFMB) tests:
The HFMB was inoculated with the batch culture and operated continuously with an influent concentration of 50 mg/L NO₃^-N an empty bed contact time of 16 hours and a recirculation rate of 286 mL/min. Once denitrification was observed, the residence time was decreased to 10 hr. A continuous flow of hydrogen gas was maintained at 10 mL/min in the lumen of the fibers. Carbon dioxide gas was supplied to the lumen every 48 hr for 1 min, to maintain the pH and inorganic carbon requirements.

Progress on Tasks
1. Sulfur oxidizing denitrification field-scale bioreactors:
Composite samples of influent to the bioreactors and the effluent from each bioreactor are collected twice every week and analyzed for:
pH (Figure 1),
Total Alkalinity (Figure 2),
NO₃^- - N (Figure 3),
NO₂^- - N (Figure 4),
SO₄^2- (Figure 5), and
COD (Figure 6)
BOD₅ (Figure 7) and
TKN (Figure 8) are monitored weekly.

2. Sulfur oxidizing denitrification bench-scale bioreactors:
Results of the sulfur oxidizing denitrifying column tests are shown in Figure 9 and Figure 10. The following is a summary of the results of these tests:

• Although denitrification was observed in the upflow sulfur-marble chip packed-bed reactors from the start of the experiment, an acclimation period with a gradual improvement of denitrification was observed over the first month.
• Denitrification rates, effluent pH and alkalinity were significantly higher with the use of crushed oyster shell, rather than limestone or marble chips. Average nitrate removal was 80% in the oyster shell column compared with 53% in the limestone column.
• Significant nitrite accumulation (up to 18 mg/L) was observed in the column utilizing limestone, while the oyster shell column had effluent nitrite concentrations below 2 ppm.
• Influent DO significantly decreased denitrification in the limestone column but did not appear to inhibit the oyster shell column.
• Backwashing did not appear to improve performance in the limestone based column.
• TOC levels similar to that of nitrified wastewater effluents did not appear to improve the effluent alkalinity in the oyster shell based column.