By Michael Rothenborg and Martin Zoffmann, October 2016
From a necessary evil to a valuable resource.
The status of wastewater has improved tremendously over the past few years. This is mainly because water and wastewater treatment (W&WT) plants have become more efficient and innovative, enhancing their processes and thus maximising output use by recovering energy and nutrients, recuperating organic matter and producing clean, reusable water – sometimes even drinkable – instead of simply regarding it as waste.
“These plants are becoming multifunctional: The original prime function is, of course, to improve public health. The biggest new value is good water resource management and a healthy natural water ecosystem,” says Mark van Loosdrecht, Professor of Environmental Biotechnology and Wastewater Engineering at Delft University of Technology, the Netherlands.
He adds that energy recovery can sometimes also be a good business case – for example, when it reduces the cost of sludge disposal. Moreover, he points out that systems that truly generate income from wastewater treatment have a major advantage because they are used not only in countries with big public sectors but also in countries where private companies handle wastewater treatment.
From sludge to heat, power and fertiliser
Global Service Line Leader at Ramboll Water, Janet Egli, sees multifunctional as “an integrated treatment approach that not only cleans wastewater but also recovers its resources”.
“Wastewater treatment used to be considered a bit of a burden, really, but as the technologies improve, more clients are becoming aware of the resources in their wastewater and recognising the potential not only to optimise their processes but also to contribute to achieving a sustainable society,” she says.
A good example of this transition is Harvest Power’s Energy Garden in Central Florida, an organics management and renewable energy facility that is the first of its kind in the USA. The Energy Garden helps businesses and communities across Central Florida reduce and reuse organic material, increase renewable energy production and revitalise soil to boost local agriculture. Restaurants, hotels and food processing facilities throughout the region are now able to send food scraps to the Energy Garden. The Walt Disney World Resort was the facility’s first customer.
“More than 100,000 tonnes of organic waste each year can now be combined with the waste-activated sludge from the local municipality and processed to produce 5.4 megawatts of combined heat and power and over 6,000 tonnes of usable fertiliser instead of being disposed of in local landfills. The overall design of the facility incorporated a mixture of both well-established and novel solutions to maximise recovery of the wastewater resources,” Janet Egli explains.
A modern plant carved into Finnish Bedrock
The plant in Blominmäki will not only treat wastewater but also produce energy. Surplus heat from the plant will be recovered from treated wastewater, and electricity produced from biogas generated in the anaerobic digestion facilities will meet more than the half of the plant’s total electricity requirement. Ramboll is assisting on the project with a range of services.
Combining waste and used water in a Singaporean mega-project
Singapore’s new Integrated Waste Management Facility (IWMF) will be the world’s largest energy recovery facility. The facility will be co-located next to a water reclamation plant, and, together, the facilities will efficiently treat the nation’s solid waste and used water, thus reaping the potential synergies of the water-energy-waste nexus. Ramboll is managing the part of the project dealing with waste, as well as providing advice on water synergies.
Copenhagen: from consumer to producer of energy
Biofos, Denmark’s largest wastewater treatment company and a longtime Ramboll client, focuses strongly on recovering gas and energy from wastewater. So, one of Biofos’ plants is now selling two and a half times more energy units than it consumes. The plant also produces around 20% of the gas used in Copenhagen’s “city-gas” system, supplying, e.g., the gas for Copenhageners’ gas cookers. The goal is to reach 60% in 2020 and hence support Copenhagen’s overall goal of becoming CO2 neutral in 2025.