RENEWABLE ENERGIES FROM WASTE WATER: A CHANCE FOR VIETNAMESE REGIONS
V. KEUTER, S. KRAUSE
for Environmental, Safety and Energy Technology (UMSICHT),
Osterfelder Strasse 3, D-46045
This article presents possible renewable energy
technologies (RET) for energy recovery from waste water worked out on the
example of two model regions of
Climate change and increasing energy consumption have to lead to
preventive use of resources. In particular in the waste water treatment and
drinking water branch, energy recovery will have to be integrated into the
different process steps in order not only to minimise the waste of energy but
also to cover the rapidly increasing energy demand, as a result of population
growth. Over 70 percent of the increase in the worldwide primary energy demand
from 2004 to 2030 will have to be met in the developing countries . The
average amount energy spent for waste water treatment varies between 30 and 60
kWh per capita and year. Currently, about 44 million people are being added to
Within the IWRM - Nam Dinh region, investigation focuses on two regions, one industrial zone (My Trung) and one rural region (Tong Xa).
According to information issued by WHO, 95 % of the urban and about 74 %
of the rural population (in
The situation in Nam Dinh regarding the health of the citizens and the pollution prevention of the environment is alarming. For the rural population in Tong Xa there are still less possibilities to get clean drinking water and vice versa to get their wastewater clean. Tong Xa is a handicraft village with small enterprises and with a high level of pollution in the neighbourhood of these small enterprises. There are only few widespread discharge systems to clean the water by buffering trough the soil, no technical facility exists to clean the wastewater. The situation of the energy supply is similar. In developing countries, energy supply often relies on various own or easily importable fossil sources. In the case of Tong Xa, most citizens have their own small biogas plant; and this biogas is used directly for cooking. Additionally, citizens often use rice straw pellets for cooking and heating. The supply of electricity is often realised via illegal connections and in small enterprises such as foundries energy is covered by different sources depending on the available source, for instance coal or gas. In Nam Dinh city, the energy also comes from fossil resources. With regard to climate change, efforts have to be made to produce energy also from renewable sources.
1. Objectives of the IWRM project
The aim of the research project in the province Nam Dinh is the development and model-based set up of wastewater treatment systems, pertaining to industrial and municipal wastewaters, each for rural and urban areas. Technological standards are lacking especially in these rural areas, which leads to significant air and water pollution. Cleaner Production (CP) measures are necessary, aerobic and anaerobic treatment processes for industrial and municipal wastewater will be planned and first steps for the installation of a pilot plant will be developed.
III. APPROACH TO INTEGRATE RENEWABLE ENERGY INTO IWRM TECHNOLOGIES
The dissemination of renewable energy technologies (RET) in developing countries is crucial for the energy efficiency and also for the active support of climate protection, being the most important goal of the United Nations’ Framework Convention on Climate Change. The use of renewable energy technologies has further benefits such as the reduction of local pollutants, allowing the electrification of rural areas without having costly investments and reducing fuel import dependency .
One of the ways to reduce operation costs and generate energy for other applications is energy recovery in/from wastewater treatment plants.
There are two approaches to include RET in wastewater treatment plants, independently of centralised or decentralised disposal structures:
§ In existing plants, optimisation of plants
§ In planning process, new design of plant
Figure 1 shows the source to produce energy in different process steps within an existing e.g. centralised wastewater treatment plant.
Figure 1. Sources of renewable energies from wastewater (acc. to )
1. Biogas: Anaerobic digestion
Anaerobic digestion is a biochemical reaction performed in the absence of oxygen by microorganisms. The process works by feeding sewage sludge to a closed reaction tank with controlled temperature in the mesophilic (30-40 °C) and the thermophilic (50-70 °C) range. The end product of the microorganism reaction is biogas and stabilized sludge. The biogas mainly composed of methane (CH4) and carbon dioxide (CO2) can be converted to both electricity and heat. The amount of gas produced depends on the amount of organic waste fed to the tank and on the temperature.
Currently, energy is generally recovered only in state-of-the-art
wastewater treatment facilities at the sludge digestion stage (heat at about 15
kWh per capita and year and electricity at about 10 kWh per capita and year).
More consequent and more efficient usage of the heat and electricity production
could double the output. In
Additional capacities could be available by using different sorts of waste, in co-fermentation processes. At present, about 25 kWh per capita and year are recovered in the wastewater treatment sector by anaerobic digestion of sludge . A surplus of about 30 kWh per capita and year from biogas out of organic matter could be generated.
2. Heating/Cooling: Waste heat from sewage sludge
The utilization of unused energy such as industrial waste heat is one important measure to save energy consumption for global warming mitigation and to reduce domestic and industrial heat waste. The waste heat from sewage sludge incineration and melting plants can be used for heating facilities and buildings. A high, however presently unused energy potential is owned by heat from wastewater (ref. to heat pumps). Energy recovery rates of about 110 kWh per capita and year can be realized by a temperature drop after exchanger modules of almost 2°C. Cooling of larger buildings is another option for this renewable energy resource.
3. Heat Pumps
range between 10 °C and 20 °C in
Flow rates of minimum 15 l/s are required to remove energy from sewers. Every litre per second of wastewater can result in heat outputs of approximately 8 kW of the heat pump. Heat recovery from larger sewers has the advantages of continuous and adequate flow rates. This concept might have the bigger potential compared to heat recovery direct from WWTPs.
4. Bio-Oil/Syngas: Transformation to oil and/or gas
Under carefully controlled
conditions and extreme temperatures of 450 to 1,000 °C sludge can be converted
to fuel in a chemical reaction. Other processes are gasification that produces
syngas which is similar to natural gas, and pyrolysis, that produces biological
oil which is similar to diesel fuel. These methods are interesting as it is a
possible alternative to sludge incineration. However, operation costs are high:
Above all, high temperatures must be guaranteed and the conditions have to be
controlled carefully, to prevent the creation of harmful by-products such as
hydrogen cyanide. Several pilot projects in Europe and the
5. H2: Hydrogen
Hydrogen can be produced from a various range of materials and it provides energy with minimal air pollution. Within the waste water treatment process the organic waste as well as the high carbohydrate wastewater from breweries could be served as a source for the hydrogen production. The conversion process / the fermentation uses bacteria which need organic parts to produce hydrogen. So far the yields have been very poor and are usually about far beyond the theoretical maximum.
6. Electricity: Microbial Fuel Cells (MFC)
Microbial fuel cells are devices using bacteria as catalysts to oxidize organic and inorganic matter and generate current. In MFCs, bacteria are separated from terminal electron acceptors at the cathode so that the only means for respiration is to transfer electrons to the anode. Electrons flow to the cathode as a result of the electrochemical potential between the respiratory enzyme and the electron acceptor at the cathode. Electron transfer from the anode to the cathode is matched by an equal number of protons moving between the electrodes so that electroneutrality is maintained .
So far, microbial fuel cells have been developed only under lab conditions which are able to run small devices such as pocket-sized ventilators.
IV. CONCEPTS AND ADAPTED MEASURES RELATED TO REGIONAL DEMANDS RESOLVING FROM IWRM – EXAMPLE TONG XA
Based on present IWRM related approaches different concepts and adapted measures for modern wastewater treatment concepts in Tong Xa village have been developed. As shown above various options exist to implement renewable energy sources in existing WWTPs. The target of new concepts should be the implementation from the very beginning. Adapted solutions should secure on the one side a reliable and save wastewater treatment and on the other side optimised energy concepts. Besides an enhanced and sustainable use of natural energy sources these concepts can guarantee an improvement in refinancing modern the increasing costs for modern wastewater treatment.
Modern decentralised approaches do consist of interdisciplinary methods and should not only focus on the single water problem. One example of modern approaches is shown in Figure 2.
Figure 2. Wastewater treatment concept in Tong Xa by use of different energy resources 
of biogas plant operation by novel DSS (decision support structures) systems
(ref. to Fig. 3) will result in cost effective wastewater treatment. Especially
industrial areas to be developed will benefit from these decisions related
Figure 3. Tool
for optimizing the operation of anaerobic treatment plants
in mixed industrial areas
As has become evident in this article, there are different options for future wastewater treatment facilities in order to cope with the demands arising from climate change and increasing commodity prices. Depending on location, legal regulations, sewer systems and specific demands, solutions range from biogas utilization to heat pumps. Before designing an energy installation, the identification of barriers is mandatory for a sustainable planning and appropriate measures at different levels (local- regional- national).
Recently, major parts of applications for renewable energies require high
investment costs, while the market energy prices for consumers of RE are -
compared to those of energy from fossil carriers- still too low in order to
create good market entry conditions and to push the use of RE. In
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