Energy

Biomass from sanitation (waste water and faecal sludge) is a promising and increasingly recognized source of renewable energy. There is an increased need and demand of resource recovery from sludge as energy for not only resource optimization but also climate change mitigation.

Relevance/Importance

The importance of energy recovery from sanitation (wastewaterWastewaterUsed water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration. and faecal sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,…) is evident from the fact that waste minimization and alternative energy generation can help in resource optimization. The advantages include associated energy cost savings, a reduced environmental impact (i.e. pollution) and compliance with strengthening regulations. The recovery of renewable energy also reduces greenhouse gas emissions and provides an option of gaining carbon credits. SludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,… streams have high calorific values and are rich in energy sources that can be potentially recovered. Energy recovery can be an incentive for complete sanitation value chainSanitation Value ChainA Sanitation Value Chain - usually referred to as Sanitation Service Chain - is defined as the combination of technologies and services that in combination manage sanitation products from their point of generation to the point of reuse or disposal. The hardware part of the… and services.

Overview

Sanitation has a strong linkage to renewable energy production and climate change. Sanitation systems can be designed in a way to produce renewable energy sources (biogasBiogasCommon name for the mixture of gases released from the anaerobic digestion of organic material. Biogas comprises methane (50 to 75 %), carbon dioxide (25 to 50 %) and varying quantities of nitrogen, hydrogen sulphide, water vapour and other components, depending on the material… or biomassBiomassRefers to plants or animals grown using the water and/or nutrients flowing through a sanitation system. The term biomass may include fish, insects, vegetables, fruit, forage or other beneficial crops that can be utilised for food, feed, fibre and fuel production.) which in turn may mitigate climate change by reducing greenhouse gas emissions.

There are different pathways for generating energy from sanitation (waste water and faecal sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,…) as briefly described below –

• Anaerobic digestionAnaerobic DigestionThe degradation and stabilisation of organic compounds by microorganisms in the absence of oxygen, leading to production of biogas. producing biogasBiogasCommon name for the mixture of gases released from the anaerobic digestion of organic material. Biogas comprises methane (50 to 75 %), carbon dioxide (25 to 50 %) and varying quantities of nitrogen, hydrogen sulphide, water vapour and other components, depending on the material… – biological conversion method which is widely used due to lower costs and ability to utilize organic waste with high moisture content without reducing the high calorific value of the produced gas (combination of methaneMethaneA colourless, odourless, flammable, gaseous hydrocarbon with the chemical formula CH4. Methane is present in natural gas and is the main component (50–75%) of biogas that is formed by the anaerobic decomposition of organic matter. and carbon dioxide).
• Thermochemical conversion producing biomassBiomassRefers to plants or animals grown using the water and/or nutrients flowing through a sanitation system. The term biomass may include fish, insects, vegetables, fruit, forage or other beneficial crops that can be utilised for food, feed, fibre and fuel production./fuel/gas – combustion (or mono-incineration), pyrolysis and gasification. These processes require lower moisture level in sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,… because energy efficiency of the process is reduced due to energy consumed for drying the sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,….
• • Incineration is one of the most prominent technology which was not traditionally meant for energy recovery but rather to reduce the volume of waste and destroy harmful contaminants. The process of heat recovery coverts the traditional incinerator into a combustor where heat is harnessed from flue gas and is utilized for heating fluid which can be used directly by heating or for generating electricity via a steam turbine.
  • In pyrolysis, combustion occurs in an inert atmosphere to produce pyrolytic oil, biochar and non-condensable gases. Biochar, non-condensable gases and bio-oil can be used as solid, gaseous and liquid fuels for electricity and heat generation via combustion. Bio-oil can also be reformed to synthesis gas for energy recovery while biochar can be utilized as soil conditionerSoil ConditionerA product that enhances the water and nutrient retaining properties of soil..
  • Gasification involves conversion of organic compounds via partial oxidation at high temperatures for production of synthesis gas which can be used in combined heat and power (CHP) for heat and electricity generation.
• Co-incineration and Co-processing – Co-incineration involves combusting sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,… (municipal) in municipal solid waste incinerators. In co-processing sewageSewageWaste matter that is transported through the sewer. sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,… serves as an alternative fuel in cement kilns and coal fired power plants. This requires additional fuel which has higher calorific value than sewageSewageWaste matter that is transported through the sewer. sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,…, but the process substitutes 15-20 percent of the conventional fossil fuels.

BiogasBiogasCommon name for the mixture of gases released from the anaerobic digestion of organic material. Biogas comprises methane (50 to 75 %), carbon dioxide (25 to 50 %) and varying quantities of nitrogen, hydrogen sulphide, water vapour and other components, depending on the material… is a renewable energy that can be used for cooking, lighting, heating and for generating electrical power. BiogasBiogasCommon name for the mixture of gases released from the anaerobic digestion of organic material. Biogas comprises methane (50 to 75 %), carbon dioxide (25 to 50 %) and varying quantities of nitrogen, hydrogen sulphide, water vapour and other components, depending on the material… production depends on the amount of organic matter removed by anaerobic digestionAnaerobic DigestionThe degradation and stabilisation of organic compounds by microorganisms in the absence of oxygen, leading to production of biogas.. BiogasBiogasCommon name for the mixture of gases released from the anaerobic digestion of organic material. Biogas comprises methane (50 to 75 %), carbon dioxide (25 to 50 %) and varying quantities of nitrogen, hydrogen sulphide, water vapour and other components, depending on the material… can either be burnt in a gas stove or used within a combined heat and power unit (CHP) for electricity generation. For use in a CHP, biogasBiogasCommon name for the mixture of gases released from the anaerobic digestion of organic material. Biogas comprises methane (50 to 75 %), carbon dioxide (25 to 50 %) and varying quantities of nitrogen, hydrogen sulphide, water vapour and other components, depending on the material… must be filtered to remove aggressive sulphur compounds. If the biogasBiogasCommon name for the mixture of gases released from the anaerobic digestion of organic material. Biogas comprises methane (50 to 75 %), carbon dioxide (25 to 50 %) and varying quantities of nitrogen, hydrogen sulphide, water vapour and other components, depending on the material… cannot be used, then it should at least be flared (this converts methaneMethaneA colourless, odourless, flammable, gaseous hydrocarbon with the chemical formula CH4. Methane is present in natural gas and is the main component (50–75%) of biogas that is formed by the anaerobic decomposition of organic matter. to carbon dioxide which has 25 times lower GHG potential than methaneMethaneA colourless, odourless, flammable, gaseous hydrocarbon with the chemical formula CH4. Methane is present in natural gas and is the main component (50–75%) of biogas that is formed by the anaerobic decomposition of organic matter.). After the generation of biogasBiogasCommon name for the mixture of gases released from the anaerobic digestion of organic material. Biogas comprises methane (50 to 75 %), carbon dioxide (25 to 50 %) and varying quantities of nitrogen, hydrogen sulphide, water vapour and other components, depending on the material…, the residue of anaerobic digestionAnaerobic DigestionThe degradation and stabilisation of organic compounds by microorganisms in the absence of oxygen, leading to production of biogas. (called "slurry or digestateDigestateThe solid and/or liquid material remaining after undergoing anaerobic digestion.") still contains all the nutrients and some organic matter. This residue is therefore suitable for application in agriculture as a fertiliser and soil conditionerSoil ConditionerA product that enhances the water and nutrient retaining properties of soil.. The macronutrients (N, P and K) which are contained in the substrates remain in the digestateDigestateThe solid and/or liquid material remaining after undergoing anaerobic digestion. and are easily available to plants. Due to the two benefits of energy production and fertiliser production, anaerobic digestionAnaerobic DigestionThe degradation and stabilisation of organic compounds by microorganisms in the absence of oxygen, leading to production of biogas. is receiving interest as an option in sustainable sanitationSustainable SanitationSustainable sanitation aims to protect and promote human health by providing a clean environment and breaking the cycle of disease. In order to be sustainable a sanitation system has to be socially acceptable, technically and institutionally appropriate, economically viable… concepts.

BiomassBiomassRefers to plants or animals grown using the water and/or nutrients flowing through a sanitation system. The term biomass may include fish, insects, vegetables, fruit, forage or other beneficial crops that can be utilised for food, feed, fibre and fuel production. is a non-fossil energy source which can substitute fossil fuels. For example, biochar is a solid material obtained from pyrolysis, the thermochemical conversion of biomassBiomassRefers to plants or animals grown using the water and/or nutrients flowing through a sanitation system. The term biomass may include fish, insects, vegetables, fruit, forage or other beneficial crops that can be utilised for food, feed, fibre and fuel production. in an oxygen-limited environment. Biochar derived from pyrolysis of sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,…, faecesFaecesRefers to (semi-solid) excrement that is not mixed with urine or water. Depending on diet, each person produces approximately 50–150 kg per year of faecal matter of which about 80 % is water and the remaining solid fraction is mostly composed of organic material. Of the total… and/or organic waste may be applied to soils in order to improve soil properties and crop yields or as a feedstock for energy recovery as well as acting as a carbon sink to reduce climate change impacts. It is typically called “biochar” when it is used as a soil conditionerSoil ConditionerA product that enhances the water and nutrient retaining properties of soil. and “char” when it is used as a fuel. Biochar has other applications such as using as an adsorption material for filters, especially for water purification purposes.

Key Actions

Step 1: Carry out a needs assessment to recover energy from sanitation (waste water and faecal sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,…). Ask key questions: is there is a need? Is there a demand and possibility to use (or sell) energy that is generated? If yes, proceed to next step.

Step 2: Conduct a feasibility study – (i) is it feasible? For example, if sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,… is largely stabilised, anaerobic digestionAnaerobic DigestionThe degradation and stabilisation of organic compounds by microorganisms in the absence of oxygen, leading to production of biogas. might not be feasible; if sludgeSludgeMixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies,… has high moisture content, thermochemical process might not be economical or should have a preceding technology to reduce moisture content. (ii) are there technologies and resources (human and financial) available for safe energy recovery? (iii) is it financially viable? Develop a business case to understand the financial sustainability of recovering energy considering CAPEX and OPEX. If there is a positive business case, proceed to next step.

Step 3: Carry out detail design and installation of the energy recovery units. Since this requires highly specialised skills, it is suggested to contact specialists or companies to carry out the detail design and installation.

Step 4: Enhance capacity of the team that is responsible for O&M of the energy recovery unit. Trainings should be provided by the specialist/company that installed the unit.

Step 5: Carry out regular monitoringMonitoringMeasures progress and checks whether a programme or intervention is working according to plan. It is the planned, systematic and continuous checking of a sanitation intervention to ensure it is doing what was intended, that allocated funds are being used effectively, that… of the unit for its long-term and sustainable operation