Xiaodi Hao, Ranbin Liu, Yu Wenbo and Shuang Li describe how new guidelines are helping China meet its ambitions for carbon reduction.
As an important part of urban infrastructure, ensuring the normal life of residents and the healthy development of the economy, the urban water sector plays a key role in sustainable urbanisation and the continuous improvement of welfare. Since the 1980s, China’s urban water infrastructure has grown and developed steadily. According to the latest statistics, water supply in urban areas of China reached up to 99% coverage during the period of the 13th Five-Year Plan, while wastewater treatment coverage and capacity reached up to 97.5%. However, China’s urban water sector is facing the challenges of being considered a high energy consumer and contributor to the country’s greenhouse gas (GHG) emissions.
Path to decarbonisation
In July 2022, the Ministry of Housing and Urban-Rural Development and the National Development and Reform Commission jointly released a document titled Implementation Plan for Carbon Peaking in Urban and Rural Development. As a key component of the ‘1+N’ policy framework supporting the ‘dual carbon’ goals of China, the plan proposes to peak carbon emissions from urban and rural infrastructure (construction and operation) before 2030. Specifically, the plan aims to promote a wide range of energy-saving technologies and to establish several targets set for specific times. The water sector, being an indispensable element of urban-rural infrastructure, is included in this ambitious action plan. Together these form the first official declaration of the Government of China to decarbonise the water sector.
Many other countries have also taken steps to pursue water sector decarbonisation, some beginning almost a decade ago. In November 2020, water companies in the UK unveiled a ground-breaking plan to deliver, by 2030, a net zero water supply and drainage system for customers, in the world’s first sector-wide commitment of its kind. Denmark, New Zealand, and several states in Australia have also set targets to achieve net zero carbon and climate neutrality in the water sector. In addition, dozens of water and wastewater utilities have joined the ‘Race to Zero’ campaign which encourages decarbonisation, aiming for net zero.
Back in China, what can we learn from these ambitious carbon neutrality roadmaps and international professionals? A thought-provoking lesson is to first realise the key role of carbon accounting practices in decarbonising the water sector. In other words, the countries or utilities outlining their roadmaps to carbon neutrality in the water sector are the ones pioneering carbon accounting.
In the UK, Ofwat, the water regulator, began to request utilities to quantify and report their carbon emissions from as early as 2007. Unfortunately, the water sector in China has very much fallen behind in quantifying its GHG emissions because of a lack of accounting methodology.
Guidelines for carbon accounting
Bearing this in mind, the China Urban Water Association (CUWA) showed foresight last year in proposing to compile local and unified guidelines to orient carbon accounting in the water sector. This compilation was the work of a group led by Professor Xiaodi Hao (an editor of Water Research) from Beijing University of Civil Engineering and Architecture. This group brought together professionals with a wide range of expertise from the academic and corporate sectors, including the Beijing Capital Eco-Pro Group, Beijing Drainage Group, SCIMEE Sci & Tech Co, Central & Southern China Municipal Engineering Design and Research Institute Co, and Harbin Institute of Technology.
The guidelines included carbon reduction strategies and pathways for the water sector to reduce GHG emissions. After several rounds of reviewing and revision, CUWA published and released Guidelines for Carbon Accounting and Emission Reduction in the Urban Water Sector. In total it consists of 10 chapters, covering general principles, urban water systems and carbon emissions, carbon accounting principles and methodologies, planning and construction, operation and maintenance, asset replacement and demolition, carbon emission reduction pathways for urban water systems, data acquisition and management, interpretation of results and reporting, and appendices. This is the first water sector-specific carbon accounting technical book published in China, to provide consistent standards and emission quantification and reporting.
The group responsible for producing Guidelines acknowledge the importance of being in line with international standards and appreciate the advancement of international carbon accounting methodologies. As such, the accounting scope, principles, and framework in Guidelines follow the established GHG accounting system – the ‘Greenhouse Gas Protocol’ and Greenhouse Gases -– Part 1: Specification with guidance at the organisation level for quantification and reporting of greenhouse gas emissions and removals (ISO 14064-1:2018), reflecting the scientific consensus. In particular, the methodologies referred to IPCC guidelines and other accounting workbooks, such as CAW from UKWIR and New Zealand. While Guidelines also follows the IPCC Tiered accuracy structure, they are not directly aligned, instead they develop country-specific methods in terms of activities, equations, and emission factors (EFs).
One of the highlights of the publication is the provision of life-cycle accounting methods covering the whole of the water sector, including:
- Inter-basin water transfer, water extraction (from surface water, groundwater, and seawater), treatment, and distribution;
- Wastewater collection (including septic tanks), treatment, discharge, and sludge treatment and disposal;
- Reclaimed water treatment and distribution;
- Stormwater drainage and management.
As Ofwat states in a report on the UK’s Net Zero 2030 Routemap, companies need to go beyond operational emissions in the water sector and tackle embedded emissions as well. Guidelines provides accounting methods for calculating emissions in the construction and demolition stages. According to the 14th Five-Year National Plan for Urban Infrastructure Construction, water supply and drainage systems will expand still further to support urbanisation. Most importantly, in this way, life-cycle concepts can be embedded and low carbon/green measures taken into consideration from the very beginning of the decision-making process. In addition, to help water utilities quantify the embedded emissions, Guidelines also provides a Quick-Calculation Sheet and Chart, based on design capacity or investment in water infrastructure.
Guidelines also pays attention to GHG emissions from sewers, particularly from septic tanks. Although the updated Standards for Design of Outdoor Wastewater Engineering (GB 50014-2021) requested cities with established wastewater collection and treatment facilities to abandon septic tanks in separate sewerage systems, hundreds of millions of facilities are still in service in China. The annual CH4 emissions from septic tanks are estimated to be 40 million t CO2-eq/a. As such, when decarbonising the water sector, septic tanks should not be overlooked and it is expected that accounting methods will need to be established for them, as well as for sewers.
Among all the emission activities of the water sector, direct GHG emissions from wastewater collection and treatment units account for a significant part of all emissions, particularly the CH4 and N2O from biological wastewater treatment processes. These are especially hard to quantify accurately due to complex mechanisms and influencing factors. This is why IPCC provides three tiered methods; Tier 2 and Tier 3 recommend applying country specific EFs to increase accuracy.
However, according to the National Greenhouse Gas Emission Inventory Reports, most countries still apply Tier 1 methods when applying IPCC’s default EFs. Only a few countries, such as Denmark and Japan, have applied their specific EFs in carbon accounting to wastewater treatment. These countries are also well known as pioneers in achieving carbon neutrality in the water sector. The compilation group retrieved and reviewed dozens of scientific papers monitoring CH4 and N2O emissions in China to estimate corresponding EFs, as well as updating the data in the IPCC’s guidelines (2019 refinement version) in terms of CH4 and N2O EFs, including the most recently published works. Thus, Guidelines also provides different CH4 and N2O EFs for different treatment processes.
Guidelines also takes non-biogenic/fossil carbon into account. The 2019 IPCC guidelines discussed possible non-biogenic CO2 emissions from wastewater treatment but did not provide an estimation method due to a lack of consensus. In Guidelines, ‘good practice’ was adopted to estimate the amount of non-biogenic CO2 emission over total CO2 emission based on its proportion in influent. A noteworthy point is that future improvements are required, along with updated information and international consensus.
The purpose of carbon accounting in the water sector is rooted in the need to guide carbon reduction. Since water companies in the UK are required to report their GHG emissions annually, they have achieved a carbon reduction of almost 50% via operational improvement and the use of renewable energy. Carbon accounting provides a powerful impetus to promote decarbonisation. To help utilities proactively clarify opportunities for reducing GHG emissions, Guidelines compiled and analysed a series of decarbonisation interventions through reviewing interventions already being implemented in the water sector. Specifically, these interventions are classified into five categories: demand control, efficiency improvement, alternative processes, renewable energy, and carbon sinks. Each intervention is analysed and discussed in terms of technical details, carbon reduction potential, net present value, and uncertainty. This is expected to guide utilities in selecting proper interventions and drafting a decarbonisation blueprint or plan.
Compared with other high-emission sectors, the water sector has advantages in achieving carbon neutrality due to the energy and resources that wastewater contains. In theory, the amount of energy recovery in a wastewater treatment plant (WWTP) should be sufficient to support the entire operation. A dozen WWTPs in Austria and Denmark have already achieved energy neutrality and even an 80% energy surplus which can be exported to the electricity grid. These advances and success stories give us confidence in the pursuit of carbon neutrality in the water sector. Indeed, the water sector in China has already been using energy-saving and recovery programmes for many years. Now, we should think bigger and – more importantly – systematically and scientifically; Guidelines is the cornerstone of China’s carbon management in the water sector, providing a fundamental tool whereby the sector can obtain further data and guide its own decarbonisation practices. •
Carbon reduction and carbon neutrality of the water sector
The current emission factors (EFs) for CH4 and N2O emissions in wastewater treatment were obtained based on 14 and 30 data by reviewing literature, respectively (2019 IPCC guidelines). Several minor errors in data citing and unit conversion (22 data) in EF-N2O calculation were identified. In addition, the literature referred to was all published before 2019, and since then a great many relevant scientific works have been published within the criteria being referred to (full-scale, with key information provided). As such, guidelines were revised to formulate new integrated EFs and EFs for different treatment processes.
The potential for solar
Many decarbonisation interventions have been implemented in full-scale water sector systems to curb carbon emissions globally. The performance of these case studies, particularly those practiced locally, can provide valuable guidance in selecting proper interventions. Summarising useful data to evaluate the application potential of interventions is an important part of Guidelines. Taking solar photovoltaic (PV) for example, Guidelines found that 22 full-scale plants have installed solar PV since 2014 – two for drinking water and the others were WWTPs. By analysing the data, the carbon reduction potential and return on investment (ROI) of solar PV are presented. As electricity generation is correlated with the footprint available in plants, which is also determined by treatment capacity, annual electrical capacity is then normalised by the treatment capacity (m3/d) to represent application potential. On average, 21.3 kWh/a electricity can be generated on a unit area matched to treat 1 m3 wastewater. The adoption of solar PV may cover 4%-37% of the electricity demand and the overall net present value is positive with an average ROI of 5%. This information can be referred to in order to carry out an assessment before implementing solar PV in plants.
