Staff Report - 11/29/2013

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Majestic Oaks WWTP
Issue: The plant does not meet effluent limits for total nitrogen (4 mg/1) and total phosphorus (2 mg/1).
Given Information: 60,000 gpd dual train activated sludge extended aeration package plant with tertiary
filters, post anoxic tank, equalization tank, UV disinfection with tablet chlorine disinfection back-up, and
ferric chloride feed into EQ tank for phosphorus reduction via chemical precipitation . Disposal is via
high rate infiltration (pond) with mechanical groundwater dewatering located 50 feet from the pond
edge. A drawing excerpt depicting the applicable portions of the package plant (EQ tank, Flow Splitter,
aeration tanks, post anoxic tanks, and clarifiers) is provided for your review
The disposal method requires removal of nitrate and phosphorus to meet effluent treatment limits of 4
mg/I total nitrogen and 2 mg/I total phosphorus.
The plant design uses post denitrification process with no supplemental carbon source.
Nitrate recycle is via 4 inch dia air lift pump with no flow measurement and no continuous flow rate
and recycle is taken from influent end of aeration basin.
Dissolved oxygen values taken by plant operator indicates that anoxic tank is not achieving continuous
anoxic conditions (less than .30 mg/I DO), see attached DO results for anoxic and oxic tanks.
The plant is nitrifying properly indicating sufficient influent wastewater volatility to achieve treatment.
The operator has asked DWQ for technical assistance with denitrification issue.
DWQ Assessment:
Denitrification: The wastewater plant design does not appear to allow easy operation of denitrification.
The mixed liquor return (nitrate recycle) is not constant flow, the nitrate recycle flow is not measured,
and it is taken from the influent end of the oxic tank. The lack of anoxic conditions within the anoxic
tanks appear to be created by carry-over dissolved oxygen from oxic zone. Additionally, the plant is not
constantly staffed during days, but visited five days per week.
Phosphorus Reduction: The operator is feeding 1 to 2 gallons of ferric chloride into the EQ tank and
effluent total phosphorus levels range from compliant to noncompliant.
Recommendation for Improved Denitrification: Obtain the services of an engineer with demonstrated
experience in the design of nitrogen reduction solutions for existing facilities. Submit a request to the
Division for design modification. Since the plant is not staffed throughout the day and only visited for an
hour or two each day for 5 days per week, an automated approach to treatment should be considered
to achieve denitrification to a maximum level of 4 mg/I total nitrogen Additionally, better flow control
though the plant is suggested as well as automated carbon source chemical feed. The writer has