US-based Cayuga Milk Ingredients (CMI) plans to manufacture a wide range of dairy products, such as pasteurized cream, whole milk powder, liquid permeate, condensed milk, skim milk powder, non-fat dry milk and milk proteins.
Cayuga Marketing LLC, a collective of dairy farmers in the Finger Lakes Region, New York, US, decided to construct their local processing plant to reduce their milk-hauling costs.
It also plans to greatly reducing transport emissions and carbon footprint as a result of the shorter transportation distances involved.
To achieve optimum environmental and efficiency benefits, CMI further decided to implement an anaerobic treatment process for its wastewater treatment facility, seeking to simultaneously achieve the most environmentally effective, energy- efficient and cost-efficient solution.
The company selected Global Water & Energy (GW&E) as the engineering, procurement and construction contractor to design, build and start up its new wastewater treatment facility.
It specified to achieve effluent discharge qualities while producing valuable biogas (methane; CH4) initially for future utilization and electricity production.
GW&E is the US branch of Global Water Engineering (GWE) and results from a joint Venture with Western Water Constructors, Inc.
Finding the wastewater treatment system for dairy plant
GWE has completed scores of successful waste-to-energy projects around the world, each one responding to the particular needs of plants ranging from sugar cane and cassava through to potato products, brewery products and any wastewater stream with a biological waste content.
GWE’s FLOTAMET system was determined as the ideal solution for wastewater treatment from a dairy plant such as Cayuga.
The system offers high rate anaerobic treatment with GWE’s ANAMIX reactor (completely mixed continuous flow stirred tank reactor or CSTR), followed by biomass recovery in a combined sludge separation system consisting of GWE’s SUPERSEP-CF, and GWE’s dissolved biogas flotation (DBF) unit SUPERFLOT-BIOGAS.
The SUPERFLOT-BIOGAS is a DBF system used for high efficiency removal of anaerobic biomass from the effluent of an anaerobic treatment system.
The anaerobic biomass is returned to the anaerobic system, thus increasing the sludge retention time.
Such systems allow anaerobic reactors to be greatly reduced n size.
In SUPERFLOT-BIOGAS systems such as that used by Cayuga, the biomass is separated by means of flotation.
Solids are forced to float by fine biogas bubbles attached to these solids.
These fine gas bubbles are created by recycling clean effluent, in which biogas is dissolved under pressure.
After injection into the lower part of the flotation tank, the pressure release results in formation of fine biogas bubbles.
Since biogas is used instead of air, the system has an enclosed design.
Managing factory discharge
The Cayuga plant is designed to treat 950 cubic meters per day (m3/d) of wastewater and 95 m3/d of whitewater (together resulting in a total contained oxygen deficit [COD] effluent pollution) load of 6,000 kg per day.
Approximately 80% of the COD load 85% of the biological oxygen demand or BOD load and is removed in the FLOTAMET system, with the waste removed converted to biogas.
This results in the production of up to 1,900 Normal cubic meter per day (Nm³/d; at 75% CH4) of biogas, with an energy content of 590 kilowatts.
The biogas will be used partially to heat up the wastewater in order to ensure optimal anaerobic digestion.
As such, the anaerobic treatment plant does not create an additional energy demand to the factory for heating purposes.
In a second phase, it is the intended to use the remaining biogas to generate electricity in order to meet CMI’s goal to further decrease the carbon footprint of the factory.
The anaerobic effluent from the FLOTAMET system is treated in a conventional aerobic treatment followed by a dissolved air flotation for solids separation.
The aerobic polishing of the anaerobic effluent ensures that the discharge from the plant to the local sewer will meet the strict discharge limits applying.
Anaerobic plants provide electricity to community, pay themselves typically in two years
Anaerobic digestion facilities have been recognized by the United Nations development program as one of the most useful decentralized sources of energy supply because they are less capital-intensive than are large power plants.
Modern anaerobic processes vastly concentrate the process in environmentally harmonious closed reactors, operated under ideal temperature and process control to optimize waste degradation and, in the process, generate large quantities of CH4 from the organic materials in the wastewater.
Savings quickly repay the cost of anaerobic plant – typically within two years – while achieving permanent environmental benefits by replacing fossil fuel.
“One ton of COD digested anaerobically generates 350 Nm3 of CH4, equivalent to approximately 312 liters of fuel oil, or generates about 1,400 kilowatt hour of green electricity,” says GWE chairman and CEO Jean Pierre Ombregt.
Anaerobic plants can also benefit local communities by providing local energy supplies while eliminating the need for large and often smelly and environmentally challenging aerobic and anaerobic lagoons commonly used outside the US.
“Applying anaerobic wastewater treatment to a food or beverage business – or any business with an organic wastewater stream – sheds a whole different light on the cost structure of wastewater treatment infrastructure,” says Ombregt.
“It can now actually become a substantial additional source of income for many factories and processing plants throughout the world, including the food, beverage and agro industry and other primary product processing.”
Story by Natascha Janssens, proposal manager, Global Water Engineering.
