by Andrew R. Delgado
• California dried fruit producer employs anaerobic bioreactor and other Siemens Water Technologies solutions to meet wastewater discharge limits
When Mariani Packing Company needed to find a solution to the wastewater treatment challenges at its Vacaville, CA, food processing plant, it ultimately chose to build an on-site treatment facility that included a number of innovative technologies.
The 100-year-old company is the largest independent dried fruit producer in the world, selling over 125 million pounds of product each year. It’s one of the leading brands of dried fruit sold in supermarkets, and the company also sells its premium fruit-based ingredients to Fortune 500 companies.
In the past, Mariani sent its wastewater to the Gibson Canyon Creek Wastewater Treatment Plant in Vacaville. But after the Regional Water Board ordered the Gibson plant to permanently close down, Mariani was left with only a few choices if it wanted to continue doing business there. One solution was to land apply its wastewater on the 300-plus acres Mariani owns next to its facility. Another option was to pay a connection fee to the city of Vacaville that would amount to tens of millions of dollars plus large monthly surcharges. The final option was to invest in building an onsite wastewater treatment system that would pre-treat the wastewater before discharge to the Easterly Wastewater Treatment Plant in Elmira, near Vacaville.
Mariani hired engineering consultants to study feasibility of land applying its treated wastewater effluent. This was not practical, however, given increasingly stringent regulations. It also would be a poor use of Mariani’s valuable real estate assets. The consultants also considered the option of paying connection fees to discharge raw wastewater to the Easterly treatment plant, but this proved too costly as well. The best option was for Mariani to build a wastewater treatment facility on its site.
In July 2005, the consultants prepared a request for quotation package and solicited proposals from five different wastewater treatment companies on Mariani’s behalf. They gave the vendors flexibility in the treatment process and process designs, but asked them to meet the following criteria:
- Provide a performance guarantee to meet the specified design parameters
- Design for future expansion to treat dissolved salts
- Demonstrate the ability to provide ongoing service and process support
- Meet a challenging construction timetable to satisfy the startup deadline
- Provide a small system footprint design
- Deliver the project on a design/build basis
“There were some challenges involved with this project,” says Bob Miller, operations manager at Mariani Packing. “Because of the project’s complexity, we needed to partner with an organization that could commission the system before our deadline to switch to the Easterly Wastewater Treatment Plant. We also needed a guarantee that the treatment process would meet the discharge limits. We ultimately chose Siemens Water Technologies because it was able to meet all the requirements for designing and building this facility.”
Mariani’s turnkey wastewater treatment system was started up in Fall 2006, ahead of the Dec. 1 deadline. The system includes many different technologies for reducing biochemical oxygen demand (BOD) of high-strength wastewater. A high-rate anaerobic Biopaq® IC reactor, provided through Siemens’ technology licensor, Paques, treats a larger amount of wastewater in a smaller footprint than competing technologies. A field-erected wastewater treatment system from the DavcoTM product line uses common wall construction for primary clarification, equalization, aeration, secondary clarification and sludge digestion. The methane-rich biogas from the anaerobic reactor will be recovered as “green” energy to run Mariani’s boiler.
The bioreactor works as follows: influent is pumped into the bottom of the vertical reactor tank and is mixed with the granular anaerobic biomass. In the lower reactor compartment, most of the organic components are converted into methane and carbon dioxide. This gas mixture, or biogas, is collected in the lower level phase separator, thus generating a “gas lift” that forces water upwards through a riser into the liquid/gas separator on the top of the reactor. The biogas leaves the reactor through this separator, and water returns through the downer and back to the bottom of the system. In the second, upper compartment, effluent is polished. Biogas formed here emerges from the polishing step and the liquid phase. It’s collected in the upper phase separator, while the effluent leaves the reactor from the top. Self-regulating internal circulation results in reduced operating costs and increased productivity and reliability.
Mariani Packing’s wastewater system is meeting the discharge limits, consistently reducing the influent BOD from 8,000-10,000 parts per million (ppm) to less than 10 ppm, and the influent total suspended solids (TSS) from 1,500-3,000 ppm to less than 10 ppm.
The treatment system is also designed for future expansion to remove dissolved salts as salinity is a growing concern for California Water Boards, which are becoming more concerned with salts contaminating water resources. Salinity levels measured as Electrical Conductivity (EC) are being imposed on industries and municipalities discharging wastewater that could make its way to a natural body of water such as a stream or groundwater table. In the future, Mariani can add microfiltration and reverse osmosis (RO) technologies to address EC regulations. The backwash water from the microfiltration system will be returned to the plant’s headworks equipment. The RO system will concentrate the salts and provide clean permeate water that will be recycled for use in the plant’s production process. The concentrated brine stream will be trucked offsite to the East Bay Municipal Utility District for discharge into San Francisco Bay. IWW
About the Author: Based in San Jose, CA, Andrew R. Delgado is a senior account manager with Siemens Water Technologies. He joined the company in 1993. With 15 years of industry experience, he has also held applications engineering and engineering management positions at Siemens. Andrew has a bachelor’s degree in chemical engineering from the University of California, San Diego.