26 January 2023
Hong Kong is upping its game and approach to food waste recycling as it seeks to improve its environmental impact and reduce the amount of organic material being sent to landfill. Hong Kong has awarded Agrivert, and two Joint Venture partners, a contract to design, build and operate an Anaerobic Digestion plant capable of processing 300 tonnes of food waste per day. Simultaneously the Hong Kong Government are devising a number of incentive schemes to ensure food waste is captured.
Whilst food waste capture and digestion may look similar to what is done elsewhere in the world, recycling the fertiliser outputs has very different challenges. The challenge in Hong Kong is that there is a relatively small land bank. On top of this, any fertilisers produced need to meet standards that exceed those traditionally seen in other parts of the world. What farms do exist are small, most of them are less than 10 ha with limited ability to apply fertiliser in volume or with traditional farming methods. Many of these farms produce quality organic produce; therefore, fertiliser quality is of utmost importance.
Agrivert needed to supply a unique solution to Hong Kong’s particular needs. It was clear that a concentrated, dry, and high-quality fertiliser was needed—the AD plant designed therefore needed to produce a product that could be marketed in Hong Kong.
Following digestion, the digestate is dewatered using centrifuge technologies similar to those seen in the water sector. A dewatered cake is then metered into driers that produce a dry digestate granulate. The granulate then needs to be upgraded to meet the fertiliser standards required in China, which involves the addition of phosphate. Agrivert has chosen to upgrade the granulate with rock phosphate, which retains the organic status of the fertiliser. Importantly rock phosphate is low in odour, unlike other organic alternatives. This allows the product to be stored and used in close proximity to the high-density population of Hong Kong.
The development of this high-value, low-odour, concentrated fertiliser that is easy to apply on small farms and within Hong Kong itself, will enable Hong Kong to move away from its dependence on fossil fuel-derived fertilisers that currently account for most of the fertiliser used in Hong Kong.