Hello, I’m Alyssa, a student in the US interning with Sustainable House, an Australian consulting business. Here I seek to answer the question: is burning 1,000 tons of food waste a week to make biogas to make electricity to power 3,600 homes in fact ‘sustainable’? Is it burning future food - when food ‘waste’ is otherwise composted to make soil to grow food?

During research into biodigestion in the US and Australia I took a close look at a biodigestion plant in Sydney and this blog is about that research. My broader research into burning wood, animal and other products in the US and Australia is in another blog here. (I use US spelling.)

Off the Parramatta River in Camellia, in Sydney, NSW, lies Australia’s first food waste-to-energy plant, EarthPower, which opened in 2003. Costing about $35 million, the plant uses anaerobic digestion to process food-related waste from solid food, sludge, liquid food, grease traps, and packaged food. It converts up to 1,000 tons of waste per week into enough biogas to power 3,600 homes at full capacity. Besides biogas, their process also makes fertilizer, air and water pollution.

Let’s see what you make of my answer here to this question: if burning food waste burns our money and future food and soil, is the process a solution or a problem?

***• EarthPower’s process of producing biogas and fertilizer***

In step 1, the food wastes are brought in on large trucks and weighed on the weighbridge. The client bringing the waste must pay a fee depending on the weight, however, EarthPower boasts that their fees are cheaper than most food waste competitors.

In step 2, the waste is separated between solids and liquids, then checked to make sure there is minimal contaminants. Once given the thumbs up, the wastes are sent into the hydropulper for step 3 to be blended into smaller pieces in preparation for the digester tank.

In step 4, the bacteria, or ‘bugs’ as EarthPower calls them, eats the wastes and produces biogas (methane). The left-over solids are called sludge. The biogas goes on to step 5, cogeneration, which converts biogas into electricity and sends it off to the energy grid.

The remaining sludge then flows to step 6, called sludge dewatering, where the thick, mud-like sludge is separated from water. Afterwards, the sludge is dried into fertilizer pellets in step 7 using the left-over heat from the cogeneration process.

The separated water, called trade wastewater, then goes through additional water treatment in step 8 and is released into the trade waste sewer.

You can see what the company says about their technology and processes here.

***• A satellite view of Earthpower (towards the bottom left) shows that it is close to the river and other industrial facilities***

***• The map version shows just how close the plant is to the banks of the Parramatta River***

Monitoring Pollution

To see if this process is the perfect solution to waste management and supplying ‘clean’ energy, there are aspects that need to be looked at closely for us to get a better view of the bigger picture.

Water and air pollution are presently the downsides of anaerobic digestion technology generally.

Under its pollution licence EarthPower supplies the NSW Environment Protection Authority pollution monitoring data from different points around the plant, including the biogas flare, biofilter exhaust stack, co-generation exhaust stack, and storm water.

Each point is monitored once per year.

• The biogas flare is constantly burning to avoid risks of explosion and is monitored for time that gas stays in storage (known as residence time) and temperature.

• The biofilter exhaust stack is monitored for carbon dioxide, carbon monoxide, sulfuric acid mist, and sulfur trioxide.

• The co-generation exhaust stack is monitored for nitrogen oxides, volatile organic compounds, as well as sulfuric acid mist and sulfur trioxide.

All the gases above are harmful to human and wildlife health, and even if they are released in small amounts, they add up. According to Valerio Paolini and her colleagues who conducted research on current knowledge about the environmental impact of biogas, carbon dioxide and nitrogen oxides were two of the main concerns.

Nitrogen oxides, sulfuric acid mist, and sulfur trioxides also contribute to acid rain, which is acidic precipitation that can fall in a wet or dry form. Acid rain is bad because it runs into streams, ponds, rivers, lakes, and oceans, changing the pH and causing the water to be overly acidic.

The surface water is only monitored for nitrogen (ammonia) and biochemical oxygen demand, which is the amount of oxygen that must be available for microorganisms in water to break down organic matter. Both are major indicators for pollution.

It is helpful that EarthPower provides the pollution monitoring data, but it is not easily understandable for the general public. There needs to be better transparency and explanations where people of all ages and backgrounds can get a good grasp of the meaning of the data without having to do outside research. For example, the greenhouse gas, carbon dioxide is emitted to Earth’s air and it would be handy for anyone to know - how much?

***• This diagram shows a map of the EarthPower plant with the locations of the monitored points marked and labelled***

Rules to Follow

For EarthPower to legally exist, there are a few licenses that they need from different organizations. These licenses lay out ground rules that the company must follow, including environmental protection efforts, noise limitations, equipment maintenance, and more.

You can check out EarthPower’s Environmental Protection License here that is issued by the NSW Environment Protection Authority. The 23-page document lays out expectations, pollution concentrations, and other limits. EarthPower must renew this document every year to keep up with changing standards.

An industrial trade wastewater license is also issued to EarthPower through Sydney Water, which is the government-owned water and sewage company that is responsible for supplying the city of Sydney and surrounding areas with clean, safe water, and which discharges the sewage to the Pacific Ocean adjacent to the city. However, through extensive online research and after emailing both Sydney Water and EarthPower, I still have not been able to access that specific trade waste license.

The final step of anaerobic digestion is when the remaining water is treated and released into a sewer as trade wastewater. That sewer leads to the Parramatta River. For any facility in Sydney to release wastewater, they must have Sydney Water’s written approval or else they will possibly disconnect their trade waste service or restrict their water services.

On their industrial trade wastewater webpage, Sydney Water acknowledges, “Accepting trade wastewater to sewer is an operational, environmental and safety risk for us.” They go on to describe what is included in the category and why they have their existing requirements and conditions.

A screenshot below from Sydney Water’s website details where trade wastewater comes from and why they have their requirements and conditions for permission to discharge trade wastewater from companies.

***• A screenshot from Sydney Water’s website***

The trade wastewater license between Sydney Water and EarthPower tells the daily discharge limits of a variety of substances, how EarthPower is charged for management fees and waste quality charges, Sydney Water’s acceptance standards, and states a requirement for EarthPower to regularly sample and analyze their trade wastewater.

A mystery remains: what is in the trade wastewater from EarthPower? Where does it go – into the adjoining Parramatta river or out to the ocean through the sewer run by Sydney Water?

According to the Sydney Water industrial acceptance standards, there are defined amounts of many toxic, harmful chemicals that are allowed to enter waterways under the license. Dangerous names like arsenic, chlorine, cyanide, formaldehyde, lead, and sulphite are included.

Although the wastewater goes through treatment, are all the impurities removed, besides the nitrogen that is included in the Environmental Protection License?

Perhaps accessing their license with Sydney Water would answer these questions. But, unlike the company’s Environment Protection Licence, the trade waste licence is not published so the impact on the river, sewer or ocean and on human health is not public.

It’s useful to consider bioenergy in the context of waste and the bioenergy sector generally - and you can read my comparison and data for the Australian and US waste problems and solutions in my blog here.

Alyssa Noble, July 2021