April 2009, Vol. 21, No.4
No-Discharge Systems for Environmentally Sensitive Areas
Since the early 1990s, the City of Malibu, Calif., has been implementing a decentralized wastewater management program as an alternative to conventional sewers. The Malibu Civic Center commercial area is adjacent to the environmentally sensitive Malibu Lagoon — the terminal point for the Malibu Creek watershed — which drains to the famous Surfrider Beach and other popular beaches. Both Malibu Lagoon and the beaches have had water quality violations related to bacterial and nutrient contamination. Total maximum daily load studies for the Malibu Creek watershed determined that nitrogen discharges associated with wastewater systems should be reduced by approximately 93%.
The proposed 6.1-ha (15.2-ac) LaPaz development in the Civic Center area consists of 11 commercial buildings comprising 12,000 m2 (132,000 ft2) of a mixture of both retail and offices and two 175-seat restaurants, with land donated for a new city hall or other municipal use. Site challenges include unique groundwater conditions and the aquifer’s limited capacity to accept wastewater discharges to maintain the required distance between the bottom of drainfields and groundwater.
To address this environmental sensitivity, a no-discharge wastewater system was prepared for the proposed LaPaz development. The system recently was permitted by the city and received conceptual permitting from the California Department of Public Health.
The no-discharge system provides septic-tank effluent collection, treatment, and effluent reuse. This system includes a recirculating media filter, denitrification filter, ozone–ultraviolet disinfection system, and polishing filter. It was sized to treat 95 m3/d (25,000 gal/d) of wastewater, with all treated effluent being reused for toilet flushing and landscape irrigation. The effluent quality will comply with California Title 22 unrestricted water reuse requirements of less than 2 nephelometric turbidity units (NTU) for turbidity, less than 10 mg/L total nitrogen, and less than 2.2 MPN per 100 mL total coliform. A storage tank will hold reclaimed water when landscaping irrigation requirements are less than reclaimed water quantities.
This system is based on a nearby wastewater system with many of the proposed unit processes and an effluent total nitrogen of less than 4 mg/L. In the 18 months of successful, reliable treatment performance, maintenance requirements for this system have been low, with only weekly 2-hour visits by the system operator. A remote monitoring system notifies operators of any emergency conditions and enables easy engineering oversight of system operations. No chemicals are used, and only normal septic-tank pumping has been performed. An additional 125 volatile, semivolatile, and priority pollutant chemicals are analyzed monthly. All have been within permit requirements, with only eight of 1984 samples being above detection limits, which are typically 5 µg/L.
In the LaPaz system, enhancements have been made to maintain reliable effluent quality to achieve the required reuse standards. The integrated wastewater irrigation system achieves the objective of minimizing water use, with an approximate 62% reduction in the estimated 140-m3/d (37,000-gal/d) potable water demand without reuse. Constructed wetlands will be used for treatment, aesthetics, and enhancing evapotranspiration to maintain a no-discharge system. All nutrients in the wastewater will be reused beneficially by the site’s landscape and thereby reduce fertilizer requirements. A wastewater salt management plan was developed to address concerns about salt buildup in soils.
Extensive groundwater modeling was performed to address quantitatively the concerns about groundwater levels. In addition, detailed hydrogeology studies determined that the sustainable wastewater project will have an inconsequential impact on area water resources. The wastewater system was integrated with landscaping plans to ensure that all treated effluent would be reused beneficially and the desired landscape palette maintained. Extensive water balance studies were performed to demonstrate that all wastewater would be used for the spectrum of expected climatological conditions and that irrigation storage-tank sizing would be adequate.
The LaPaz project will demonstrate that decentralized distributed wastewater systems can be as effective as centralized facilities in achieving the accepted limit of technology for nitrogen removal, treating for microconstituents, and achieving standards for unrestricted water reuse. In addition, the system is fully compatible with beneficial reuse of all treated wastewater, resulting in a no-discharge system.
Pio Lombardo, former chair of the Water Environment Federation (Alexandria, Va.) Small Community Committee, is president of Lombardo Associates Inc. (Newton, Mass.).