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Water Resource Recovery Facility (WRRF)

The Graton Community Services District had just been formed July 1, 2004 when the Regional Water Board issued a Notice of Public Hearing for October 6, 2004 to upgrade the water resource recovery facility (WRRF) from secondary to tertiary discharge standards.  Graton’s collection system and secondary treatment plant were built in 1979 by Sonoma County Department of Public Works. In 1995 Sonoma County transferred all wastewater plant operations to the Sonoma County Water Agency.  SCWA agreed in 2004 to transfer the Forestville and Graton plants to local control. Sonoma County Water Agency continued to operate the plant through the first year to allow GCSD time to build the management and operations structure to assume operational control. 

Graton CSD Water Resource Recovery Facility

Lescure Engineers had already commenced design of a flood wall when six months into GCSD’s control Mother Nature delivered a flood on January 1, 2006.  Following our initial application in August 2006, the following denials, and two appeals for FEMA funding, GCSD completed construction of its Flood Works Project in November 2010 to protect the existing treatment ponds and the anticipated treatment upgrade.  In March 2014 GCSD will commission its upgraded WRRF to begin producing Title 22 Tertiary Disinfected Effluent. Graton’s initial Board of Directors adopted a policy to maximize land discharge with the objective of sustaining the local watershed.  The Community’s original vision had been complete effluent dispersal to a redwood forest planted on its pasture lands and nearby agricultural operations.  While land dispersal remains as District Policy, limited land dispersal capacity and the Regional Water Board’s Order No. R1-2004-0038 to upgrade stream discharge to tertiary discharge standards by August 1, 2007 required the District to upgrade the treatment process at the earliest possible date.  Order No. R1-2012-0016 reset that compliance date to April 30, 2017.  Another design criterion added  by the District’s General Manager, Bob Rawson was to achieve a “complete-removal” system which leaves no residuals which would require further treatment or cleanup.  

Schreiber Fuzzy Filters

In response to the Regional Water Board’s Order, GCSD has implemented a unique treatment process for upgrading secondary aerated lagoon effluent to tertiary standards.  Before considering the means for achieving tertiary effluent standards Lescure Engineers examined the capability of the existing treatment ponds.  We determined they have sufficient biological treatment capacity to deliver effluent meeting the numerical biochemical oxygen demand (BOD) limits for tertiary effluent without any adaptation. Initial operations of the tertiary system have confirmed that capabiltiy. 

Since Graton’s General Manager had negated membrane technology for the tertiary treatment chain we were faced with the challenge to specify an alternative to that prevalent technology.  We investigated various cloth membrane and media depth filters, settling on the Schreiber “Fuzzy Filter” because it provided a robust, simple depth filter with low energy and maintenance requirements. It is however certified for Title 22 treatment of activated sludge effluent which contains relatively large particles, where pond effluent contains large amounts of algae small enough to pass through the Fuzzy Filter.

Heron SAF

Our solution to this dilemma lay in the Heron “Suspended Air Flotation” (SAF) technology.  The SAF uses flocculants and coagulants to “glue” the algae particles together, and surfactant agent to create froth which “floats” the algae and microbial floc out of the wastewater stream.  Lescure Engineers’ pilot test conducted in June 2007 found the combination to perform very robustly. The SAF performed equally well with both settled and un-settled pond effluent as a “roughing filter”.  The Fuzzy Filter reliably produced long filter runs with effluent turbidity better than 1 NTU where the Title 22 standard is 2 NTU. This is the SAF’s first installation in municipal wastewater service where it has previously been deployed only in industrial applications. 

The Graton WRRF is also the Fuzzy Filter’s first application to pond effluent, enabled by coupling it with the SAF as a conditioning mechanism and roughing filter.

PTG Pasteurization Disinfection Unit
Piping from Fuzzy Filter to PTG Unit & Generator
Piping from Fuzzy Filters to PTG Unit & Generator

Two more unit processes complete the tertiary treatment chain; disinfection and biosolids management.  Where Graton has historically disinfected with gaseous chlorine it will now employ the first-in-the-world application of pasteurization technology for municipal wastewater. Pasteurization Technology Group (PTG) certified its technology for Title 22 service in 2007.  In addition to disinfecting the effluent, the PTG technology generates 30 KW of electricity rather than consuming electric power as UV disinfection does. Pasteurization also eliminates formation of chlorine disinfection by-products, the cost of monitoring effluent for disinfection by-products, and the risks of storing and handling chlorine.

 

The final unit process employs composting to stabilize the biosolids into a valuable product which can be safely utilized by the general public.  The SAF removes biosolids from both the main effluent stream and the Fuzzy Filter backwash stream.  The SAF “float” proved easy to dewater in the pilot test and now in the initial days of service.  Biosolids are removed from the stream and dewatered to composting standards by gravity without imposition of any further technology.  Where dewatering of activated sludge effluent typically requires a centrifuge, screw press, or gravity belt press Lescure Engineers saved the District $250,000 by eliminating such technology.  The SAF float is pumped into a field bin where it drains passively by gravity to the dry solids content level suitable for composting.  This step is key to achieving a “complete removal” process rather than returning constituents to the treatment process as many plants are forced to do. 

Lescure Engineers designed a custom composting facility scaled to Graton’s WRRF capacity.  This facility is a hybrid, combining features of open static piles and the automated facility at Santa Rosa’s Laguna plant for which the capital cost can only be justified for such a larger facility.  The Composting Facility provides permanent structural cover with capacity for 80 days production to yield a fully finished US‑EPA Class A-EQ compost. The permanent cover controls potential contamination from runoff, and eliminates the labor costs of dealing with temporary cover. The geometry of the facility with internal “push-walls” dividing it into quadrants, facilitates turning of the compost with a tractor loader without the cost of specialized equipment as can be justified for a larger facility.  The first quadrant provides sufficient capacity for the 20 to 25 day initial period to achieve US‑EPA Class A-EQ standards. The remaining 3 quadrants provide additional time for aging and screening to produce the finished product.

Each of the equipment manufacturers; Heron, Schreiber, and PTG has their own proprietary control programs which Lescure Engineers integrated in accord with the performance parameters determined by the plant operations, and specified by the Waste Discharge Orders and the conditions for Title 22 certification.  Ed Myers, Systems Process Engineer with Lescure, prepared the Process Control Narrative (PCN) to direct the package integrator, Telstar in writing the SCADA programs.  Ed is deeply familiar with the SAF and Fuzzy Filter operations as he conducted their full-scale pilot testing in 2007.  The SCADA program performs historical process data trending and graphics presentation while coordinating the relay logic panel for the SAF, and the two programmable logic controllers for the Fuzzy Filters and PTG pasteurization system.  The control system works around the clock, incorporating features for monitoring performance and sending alarms to the Operator on-call.  In the event Operators are unable to respond timely, programming and mechanical features are built-in to the system to shut-down in a fail-safe mode without compromising effluent discharge quality.  As with any SCADA system, Operators will pull historic data reports, both to gain detailed insight to optimize the system’s performance and to prepare monitoring reports to the Regional Water Board.

In summary, Lescure Engineers has met its clients objectives within the constraints imposed by regulations and compliance schedules.  We have succeeded in applying innovative technologies in a first-in-the-world system which produces two valuable products; tertiary disinfected reclaimed water, and compost suitable for unrestricted application.  We have succeeded in realizing the  General Manager’s objective to achieve a “complete-removal” system which leaves no residuals which would require further treatment or cleanup.  We anticipate this system will be a boon for secondary pond systems required to upgrade to Title 22 Disinfected Tertiary Effluent standards to meet increasingly stringent discharge requirements. The pasteurization element will provide even greater advantages when effluent discharge standards begin to address and prohibit chlorine disinfection by-products.


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