Human wastewater treatment - without the CO2. by CO2nfluence
Human wastewater treatment without the greenhouse gases; a CO2-neutral, economically competitive approach to wastewater treatment.
In an attempt to solve the problem of human generated waste emissions, CO2nfluence has developed a CO2-neutral integrated human wastewater treatment solution integrating waste (human wastewater, food waste, and paper waste) disposal and heat and power production through the combination of anaerobic digestion technology, algae cultivation and electricity generation via a solid oxide fuel cell.
This system targets human wastewater generation which contributes to roughly 2% of global yearly greenhouse gas emissions (IPCC 2007, IEA 2012), and post-consumer organic waste such as food and paper waste that is sent to landfills, generating emissions, which when combined with human wastewater specific emissions contributes to roughly 5% of global GHG emissions - 50% of which can be attributed to CH4 emissions from landfill (IPCC 2008).
The proposed technological solution consists of four integrated systems: anaerobic digestion of human and other biodegradable (food, paper) waste to form biogas, algae cultivation for CO2 fixation and liquid waste purification, biogas cleaning and CO2 recovery, and electricity generation from generated biogas. CO2e reductions are achieved by this self-sustained, CO2-neutral treatment process through the offsetting of CO2e emissions from traditional wastewater treatment plants, and the offsetting of fossil-based energy usage (electricity and heat) via electricity and heat production from generated biogas.
Category of the action
Reducing emissions from waste management
What actions do you propose?
The CO2nfluence wastewater treatment process is designed as an alternative to traditional wastewater treatment plant technology, with the aim for this sustainable wastewater treatment solution to be adopted as the technology of choice in all future wastewater treatment plant developments. Direct impact on climate change will be achieved by governments, municipalities and private wastewater treatment facilities adopting the proposed wastewater treatment process, with the CO2nfluence team acting as designers of the tailor-made system solution in order to provide wastewater treatment CO2 neutrality and CO2 displacement through the following processes:
After collection of the toilet wastewater, the solids (faecal matter and toilet paper) are given sufficient time to settle in a standard settling tank. From here, the solids are withdrawn from the underflow and mixed with biowaste (food waste as well as unrecyclable paper waste) before they are pumped through a heat exchanger to raise the temperature up to the 60°C, which is the required temperature for optimal thermophilic digestion as well as the elimination of pathogens from the waste (Willis et al 2005). In the up-flow anaerobic digester (UASB) the toilet solids, biosolids and harvested algae are co-digested to produce biogas, which is collected from the top of the digester, compressed and sent to the first CO2 absorption column. The liquid effluent from the digester is sent to a centrifuge to produce a thickened sludge, of which 60% is recycled to the digester to provide an overall solids residence time (SRT) sufficient to remove approximately 70% of the solids. The remaining sludge is then sent for final drying in preparation for incineration, and the clarified liquid from the centrifuge is sent to the nutrient recovery section.
Sludge Treatment and Nutrient Recovery
This concentrated sludge, consists of about 25% solids, and a nutrient-rich liquid stream. The portion of sludge which is not recycled to the digester is then prepared for incineration by drying in a spray dryer, whilst the nutrient-rich liquid is separated by a membrane into a clear water stream and a concentrated stream. The heat produced from incinerating the dried sludge solids is used to provide heat for the customer, and the resulting ash is collected and could be used in the concrete industry (Cheremisinoff 2002, p. 555). The clear liquid stream leaves the process as treated water fit for recycling as non-potable water, and the nutrient-concentrated stream is collected to be sold as liquid fertiliser.
The biogas produced in the anaerobic digester is compressed and sent to the Biogas Cleaning stage. The purpose of this part of the plant is to remove as much CO2 from the biogas as possible so that it can be used for algae growth in the photobioreactors. In addition to CO2, other impurity gases in the biogas such as H2S and NH3 are removed, further purifying the biogas so that it can be used directly for cooking or heating, or in the SOFC for electricity production. The removal of CO2 is performed with a two-stage high-pressure absorption process with wastewater, taking advantage of the difference in solubilities of CO2, H2S, NH3 and CH4. As a result of the biogas cleaning stage 94% of the CO2 in the biogas produced by the digester can be recovered and used for algae production, whilst only 6% of the methane is lost to the algae stream.
Algae Cultivation and Harvesting
The algae cultivation and harvesting system is at the heart of the CO2fluence process. Algae cultivation not only cleans the water (by absorption of N, P and metals), it also absorbs the CO2 removed from the biogas, thereby providing additional biomass for digestion and renewable energy production. This system utilises a photobioreactor to ensure controlled-operating conditions, with the algae produced in the system concentrated in a coalescer and sent to the anaerobic digester as fuel for biogas production.
The composition of the cleaned biogas leaving the second stage absorption column (COL2) is approximately 95% CH4, 4% CO2, with trace amounts of other gases. This gas could be used directly by the customer for cooking or heat depending on their requirements; however, the standard CO2nfluence process uses the energy in the methane by generating electricity in a SOFC. After leaving COL2, the biogas is sent to a pre-reformer (PREFORM) which pre-reforms some of the methane fuel. The steam needed for reforming and water-gas shift reactions in PREFORM is provided by recycling and mixing a portion – typically 60% – of the SOFC anode gases with the fresh fuel entering the pre-reformer. From the pre-reformer, the fuel enters the anode of the SOFC stack where reforming is completed and electrochemical oxidation of the hydrogen product takes place. The SOFC operates at a temperature of 910°C and a pressure of 2 atm. Air is supplied to the SOFC cathode by a compressor.
The CO2nfluence team has already completed computational and scenario modeling of the proposed system, with small-scale and subsequent large-scale system construction and testing required to physically verify the viability of the system.
In terms of adoption of the system, on a public-level, given that the system is calculated to be cheaper than traditional wastewater treatment plants (see the cost section of this proposal) no new economic incentives will be required, and those that already exist will be required, but to a lesser extent. On a commercial-level, if private companies/industry is to adopt this technology (and take the burden away from centralised municipal wastewater treatment plants), the same economic incentives and policies directed towards traditionally public-run wastewater treatment plants would need to be directed towards systems run by private companies.
Who will take these actions?
In terms of uptake and operation of such systems, the water and wastewater treatment branches of governments and existing wastewater treatment organisations (both public and private) will be required to purchase and install these systems. Furthermore, discussions between these government departments and the CO2nfluence team would be required to determine any legal issues that could affect the implementation of the proposed wastewater treatment system.
In order to further develop this technology to the point where it is able to be realised physically, the CO2nfluence team will need to complete further research and modeling, followed by small-scale and subsequent large-scale physical testing of the design. Furthermore, research institutions (such as universities and R&D centres) will be vital in providing a knowledge pool for such research and development, whilst the CO2nfluence team will need to develop relationships with equipment manufacturers to ensure optimal interoperability between the key components of the system.
Where will these actions be taken?
In the initial phase of system implementation, the initial rollout would be in Europe, where there exists a government-mandated need for more efficient, wastewater treatment technology across a large market. New laws and international environmental agreements have led to gradual changes in industrial practices within Europe, with a trend towards cleaner production systems with lower environmental impact. We believe that this current “green technologies” trend will provide CO2nfluence with greater access to customers, due to the greater openness of governments/municipalities towards sustainable technologies due to government legislation.
More specifically, the initial focus is on countries with high solar irradiation (as light is required for the algae growth, and use of natural lighting would reduce system costs regarding artificial lighting) and which are in the process of switching to “greener” technologies. Based upon these aspects, the most promising locations for our system within the European market would be Spain, Portugal, Italy and Greece, which are poorly ranked in terms of wastewater management in Europe, and which have the greatest exposure to solar irradiation in Europe (European Commission 2013).
Upon successful development of the system in developed countries, such as southern Europe, developing regions would be targeted due to their higher CH4 and NOx emissions from wastewater and human sewage than developed countries, resulting from their rapid population growth and urbanisation which has left the development of wastewater infrastructure struggling to catch-up (IPCC 2007). Potential target countries would include China, India, Turkey, Bulgaria, Iran, Brazil, Nigeria and Egypt, as their CH4 emissions from wastewater are the highest in their respective regions, whilst they also have high levels of solar irradiation. Australia also has potential due to the availability of sunlight and need for decentralised waste treatment facilities.
What are other key benefits?
Whilst the level of the additional benefits would be site-specific, they include:
- Water savings – achieved via the recycling and reuse for human waste disposal (i.e. grey water for toilet flushing);
- Energy Savings – surplus heat and electricity generated from the process can be used by the facility for other operations, leading to energy savings, and;
- Nutrient recycling – treatment process concentrates nutrients (such as phosphorous) out of the waste, enabling them to be reused internally or externally i.e. as fertilisers for agriculture or to support algae growth
These by-products contribute to the holistic viability of the product solution by adding to the total value proposition of the proposed product, and providing a strong foundation for the financial viability of the concept.
How much will emissions be reduced or sequestered vs. business as usual levels?
Conservative case – low CO2e emissions from grid electricity (taken as the Dutch value 0.4755 kgCO2e/kWh) (AEA 2012), a country with a mature waste management policy (3% Landfill, 97% incineration of organic waste), and the lowest value in the range of per capita WWTP emissions found (0.198 kg CO2e/PE/d). Emission reductions of 159kg.CO2e/PE/y.
Typical case – moderate CO2e emissions from grid electricity (taken as the Czech value 0.6025 kgCO2e/kWh) (AEA 2012), a developing waste management policy (67% Landfill, 33% incineration of organic waste), and the median value in the range of WWTP emissions (0.489 kg CO2e/PE/d). Emission reductions of 292kg.CO2e/PE/y.
Optimistic case – high CO2e emissions from grid electricity (taken as the Australian value 1.00423 kgCO2e/kWh), a country using predominantly landfill (90% Landfill, 10% incineration of organic waste), and the highest observed value in the range of WWTP emissions studied (1.36 kg CO2e/PE/d). Emission reductions of 642kg.CO2e/PE/y.
What are the proposal’s costs?
The overall capital costs required for the system represent the combined total of all equipment costs, in addition to ancillary costs pertaining to miscellaneous equipment and the installation process costs. The combined capital cost totalling roughly 970 euros per person equivalent capacity (€970/P.E-capacity) of the system (as based on the theoretical 45 000 P.E system used in all system modelling), with the capital costs based on Peters, Timmerhaus and West (2003), but updated to 2013 prices.
Furthermore, based on a scenario for the purchase and operation of a 45 000 PE capacity system, assuming the entire capital cost of the system was taken out as a loan (assuming 3.5% interest rate), it is calculated that in order to cover all O&M costs, in addition to interest and principal repayment costs, that an additional ongoing costs of €54/P.E-capacity/year would be required.
One-off capital investment costs: €970/P.E-capacity.
Ongoing costs: €54/P.E-capacity/year.
- CO2nfluence will focus on further developing its CO2-neutral wastewater treatment system design, focusing on improving system (and economic) design and performance, in addition to developing relationships with key government and wastewater industry partners.
- CO2nfluence will seek to initiate and successfully complete small-scale physical trials of its system, focusing on assessing the transition from theoretical to physical operation of the CO2nfluence system, and on the steps necessary to achieve future full-scale system operation success.
- Completion of the small-scale physical trial would result in progression to a large-scale facility trial in cooperation with a municipality wastewater treatment department.
- Upon successful operation of the large-scale test facility, the proven concept would be pitched to all governmental/wastewater partners in the initial target market of southern Europe, followed by other developed nation markets.
- If southern European market entrance is successful, focus will be turned to other developed markets with suitable environmental conditions, e.g. Australia, southern United states.
- Assuming acceptance as a wastewater treatment system in developed countries, the system would be tailored to meet developing countries’ needs, with emphasis on overall cost reduction to increase affordability.
- Medium-term markets would include China, India, Turkey, Bulgaria, Israel, Iran, Nigeria, Egypt and Brazil.
- In the long-term, it is hoped that this process becomes the industry standard world-wide for wastewater treatment, and that all wastewater treatment systems, both in the developed and developing world will adopt this type of system.
- Within 50-100 years it is hoped that the phase in of this technology (and similar concepts) will result in net global CO2e emissions from wastewater treatment of zero, in addition to significant savings in water usage, and nutrient recycling (i.e. nitrogen, phosphate).
AEA 2012, Guidelines to Defra / DECC's GHG Conversion Factors for Company Reporting, viewed 2 May 2013, <https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/69554/pb13773-ghg-conversion-factors-2012.pdf>.
Cheremisinoff , NP 2002, Handbook of Water and Wastewater Treatment Technologies, Butterwoth-Heinemann: USA.
European Commission 2013, Directive 2008/98/EC on waste (Waste Framework Directive), European Commission, viewed 13 March 2013, <http://ec.europa.eu/environment/waste/framework/index.htm>.
Intergovernmental Panel on Climate Change (IPCC) 2007, Emissions Trends, viewed 28 February 2013, <http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch10s10-3.html>.
Intergovernmental Panel on Climate Change (IPCC) 2008, Technical Summary, Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK.
International Energy Agency (IEA) 2012, CO2 Emissions from Fuel Combustion: Highlights, viewed 28 February 2013, <http://www.iea.org/CO2highlights/CO2highlights.pdf>.
Peters, MS, Timmerhaus, KD and West, RE 2003, ‘Plant Design and Economics for Chemical Engineers’, McGraw-Hill, New York.
Willis et al 2005, Advances in Thermophilic Anaerobic Digestion, Brown and Caldwell, viewed 31 May 2013, <http://www.brownandcaldwell.com/tech_papers/advances%20in%20thermophilic.pdf>.