Reforestation with Biochar in Hong Kong
Reforestation of Hong Kong is a large intractable problem that the Kadoorie Farm and Botanic Garden is tackling with the help of biochar. The Kadoorie Farm and Botanic Garden (KFBG) is a unique botanical gardens tucked away in the highlands of Hong Kong (HKG). Established in 1956, the KFBG site is one of Hong Kong’s little known jewels. Nine kilometres of road wind their way up around organic farming terraces, botanic gardens and native forest to the summit of the mountain (Kwun Yum Shan) at over 1800 ft above sea level. A wide variety of educational displays, sustainability features and wildlife rescue facilities complement the extensively landscaped gardens with their cobbled paths, pavilions, bridges, waterfalls and picnic spots. Allocated a significant area of land of over 250 ha this botanical garden is a cool, green forestry reserve for animals – and humans alike!
Recently, KFBG’s Flora Conservation Department launched a world first program to address two key pressing issues at the gardens: improving the heavily eroded soils at the elevated levels of the mountain tops, and woody weed removal and disposal from within the botanical gardens. The new program builds on smaller test projects and has now moved to a full-scale program to convert the woody weeds to biochar, and then utilise the biochar on the mountain sides to help with restorative efforts.
Historically, the natural environment of HKG experienced large scale deforestation as a result of extended human settlement – almost the entire region was deforested over a 2000 year period. The arrival of British rule saw a concerted effort to implement reforestation programmes in various areas. The impact of WWII saw these efforts temporally undone, but post war efforts saw reforestation programmes resume and continue to present day. By 1990, almost 10% of the HKG was covered by woodland, 5% by plantation and around 10% by tall scrubland. Non-native species planted under British rule are a dominating presence of the natural landscape, which has introduced other environmental issues such as habitat loss for native fauna, and mono-culture woody species.
The hillsides of KFBG were not spared the impacts of historical deforestation, and significant efforts of restoring these highland zones have occurred over the past few decades, but with limited success. The windswept underlying granite rocks are scantily covered with soil and are overgrown with grass making tree establishment very difficult. KFBG launched a programme several years ago to apply biochar to their denuded hillsides to assist with tree planting efforts. The water, nutrient holding capacity and structure of biochar was appealing for helping with tree establishment. A small biochar kiln was implemented for on-site production and this was sufficient for initiating small and successful trials. However, to implement a solution that could cover an entire mountain top with biochar a large scale solution was always envisaged.
KFBG also had another problem with large biomass residues from their garden forests and clearance efforts of non-native acacias and eucalypts from their land. The landfill disposal of large amounts of unprocessed biomass is prohibitively expensive in HKG and so this represented a significant challenge for the botanic garden. This is where biochar comes into the story.
Biochar was a logical solution for such a set of problems. The large volumes of waste woody biomass from the restored forests could be pyrolysed and turned into valuable biochar for addition back to the soil on the mountain tops. The biochar added would improve plant growth but also help lock nutrients and moisture in the soil as well as improve its structural properties, aiding in the prevention of erosion. KFBG investigated options for large volume biochar supply from the commercial market vs an internal production programme. The commercial market was deemed too expensive especially considering transportation costs, and the sustainability of product was not assured in some cases. An in-situ production process was deemed the best solution.
KFBG conducted a world-wide search for suitable technology and identified the CharMaker MPP20 produced by Earth Systems as a size class and price point that would best suit their requirements. The ability of the technology to process woody biomass without the requirement for chipping of the trees was very appealing, saving time, costs and OHS issues for preparing the feedstock.
As part of due diligence, KFBG management visited Australia to observe two CharMakers in operation at a production site in a rural setting. The CharMakers were processing residue Willow trees harvested from riparian land care efforts. The CharMaker MPP20 is a mobile batch pyrolysis unit designed to efficiently and cleanly pyrolyse a large amount of biomass feedstock and convert it into valuable biochar. The design is based on a shipping container layout and is easily transported despite the large amounts of biomass it can handle. The CharMaker technology was first deployed in 2011 and has been trialled on over 40 different feedstocks from African Mahogany, hay, to railway sleepers. A thermal oxidiser efficiently removes smoke emissions during operation making it an almost smokeless technology that meets Australian emissions standards. Several units are in operation in Australia, and KFBG visited the Victorian based units.
KFBG proceeded with a CharMaker FPP20 (fixed pyrolysis plant – 20” container size) solution and this was soon delivered as a fully functioning unit to a prepared site in the botanic garden. Soon the waste biomass was being pyrolysed and large quantities of biochar were being produced – about 1.2 tonne dry basis per batch, or 5 m3. Once the pyrolysis process is complete, the biochar is quickly removed and quenched. The biochar is unloaded into a concrete bay where it is crushed prior to transport to the mountain hill-sides for application.
Earth Systems staff travelled to Hong Kong to help train the workers on how to use the machine and now the two workers at the botanic garden are fully trained and able to produce the biochar themselves. The machine incorporated innovative technology such as a built in drier unit which utilises heat from the thermal oxidiser to dry out other wet biomass to make it more suitable for pyrolysis in the main unit (or for kiln drying other materials). The CharMaker also contains an internal bio-oil collection system composed of numerous fractions and chemicals. The aqueous fraction, sometimes called “wood vinegar”, may have numerous agricultural applications, from enhancing germination rates to acting as a pesticide. The pesticide effects of wood vinegar were appealing as this natural organic product was enabled for use on the site (as opposed to introduced commercial chemical products), and trials are currently underway for use of this product. The bio-oil product is currently under consideration as a thermal energy source for the site. The ability to produce their own liquid fuel on site (their own bio-refinery!) is appealing for KFBG and meets their sustainability criteria.
KFBG are also investigating the use of heat generation from the thermal oxidiser unit to try and make the process more sustainable and obtain not only char and useful liquids from the process but also a source of energy. Earth Systems are still actively involved in the project with ongoing site visits for support. As well, the CharMaker was installed with the standard on-line connectivity package – this enables KFBG continue to operate the CharMaker FPP20 with on-line monitoring and control (as needed) from Earth Systems engineers in Australia.
The biochar is now being used as part of the forest restoration work, helping improve the structure of the soil, enhance its nutrient and water holding capacity as well as helping prevent erosion. Over time the forests will start to grow on the hillside, biodiversity will start to increase, and soil erosion and landslides will become a thing of the past. Biochar will hopefully support this positive environmental outcome to occur.
For more information on the KFBG project please visit here.
For more information on the CharMaker unit please visit here.
And please see below for an interesting video of the project:
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|Case Study – Turning Waste into Biochar||Botanic Gardens Biochar Production||Pyrolysis Liquids and ‘Wood Vinegar’|