Development of a wastewater switch for the energy-efficient selective partial flow treatment of highly concentrated wastewater (ESTA) at municipal wastewater treatment plants
The research association ESTA is a merger of AKUT Umweltschutz Ingenieure Burkard und Partner, the Technical University of Berlin, FG Siedlungswasserwirtschaft and LAR Process Analysers AG. The aim was the development of an intelligent wastewater switch in the inflow of municipal sewage treatment plants for the separation of highly charged inflows and energy recovery by means of anaerobic treatment. The joint project “ESTA (FKZ 02WQ1382A-C)” was funded by the Federal Ministry of Education and Research (BMBF) within the framework of the SME-innovativ funding initiative.
As a result, peak inflow concentrations could be identified and evaluated with a time resolution of 6 minutes with regard to height and frequency in order to activate the wastewater diverter.
A successful operation of the wastewater switch and the anaerobic test reactor was possible despite the low peak concentrations and the low number of shock loads on the investigated wastewater treatment plant in combination with excess sludge. The simulation of the wastewater treatment plant showed that, despite the removal of the highly charged wastewater fraction and despite changes in the C:N ratio, the statutory monitoring values can be complied with under the underlying conditions (in particular the low ammonium inflow values). A maximum degree of electrical self-sufficiency of 75 % could be achieved.
A central component of the project was the construction and operation of a test plant at the Baruth (Brandenburg) sewage treatment plant, which was planned and installed in coordination with the project partners TU Berlin and AKUT. The project partner LAR was mainly responsible for the development of an adapted online analysis technology. Project start was 01.10.2016, project end was 31.03.2019.
With the help of the TOC-Online monitor a mechanism was controlled, which feeds inlet water of the sewage treatment plant to an anaerobic reactor from an adjustable threshold concentration. Both the analysed feed concentrations, the volume flows and loads fed into the reactor and the biogas produced in the reactor were evaluated.
Due to the implementation of the TOC online monitor on a trailer, the measuring equipment is now also available for mobile use. Measurement campaigns at other sewage treatment plants and at two industrial sites prove the operational capability. The basic load could be clearly determined and the concentration peaks could be evaluated with regard to height and frequency. It was possible to define threshold values in concentration and volume of an impact load which makes the investigation of a general conversion of the process with separate anaerobic sludge treatment useful.
“Although the Baruth wastewater treatment plant under investigation with the evaluated impact loads is below the threshold values determined and a further investigation does not appear to be appropriate here, the results of the other sites investigated certainly show potential”, explains project coordinator Dipl. Ing. Thilo Burkard (AKUT).
The participating project partners are accordingly optimistic that the new concept can be applied to new construction and conversion of wastewater treatment plants. A measurement campaign with the mobile measuring device is therefore planned for other wastewater treatment plants.
Further information: Thilo Burkard
Thousands of canals run through the cities in China. In the shallow estuaries of the major rivers, they have traditionally served as traffic routes navigable by barges. With rapid and extremely dense development, the drainage of water became increasingly important. However, this was accompanied by ever-increasing pollution. Hydraulically overloaded sewers and high material loads in rainwater runoff today lead to excessive pollution of surface waters. This has a bad effect on their oxygen balance, which leads to serious odour nuisance, especially in the warm season.
Since the government declared the remediation of these waters to be a central task for all municipalities, many technologies have been tested. In most cases, however, success has not been achieved. Obviously, the problem could not be solved by internal measures in the waters alone. In two cases, retention soil filters were now used, which are suitable for the short-term absorption of high hydraulic loads from the combined sewer and stormwater system and thus for treatment before overflowing into the sewer.
Within the framework of the BMBF-funded KEYS joint project entitled “Pioneering technologies for the sustainable management of urban watersheds as a key factor for the successful implementation of the “sponge city” concept”, the effect of these systems is to be demonstrated and investigated in parallel. Retention soil filters were developed in Germany and represent the key technology in this country for both centralised and decentralised treatment of rainwater and combined sewer overflows.
The engineers of AKUT, who have been working in China as consultants for 10 years, are aware that German technology cannot always be transferred one to one abroad. In particular, the data basis for optimal dimensioning is often missing there. In cooperation with the project partners, the prerequisites are now being created. During our visit in December 2019, the sampling locations for the planned measurement campaigns in 2020 were examined and operational data were obtained. The installation of online probes and rain recorders was prepared.
The two demonstration sites, each with 3 000 m² retention filter area, are located in Suzhou, Jiangsu Province. While the first retention soil filter at the Zhujing Channel has been in operation since 2018, the second filter at the Hongshuanglou Channel was not completed until winter 2019.
In contrast to the more water-rich regions, these soil filters will also be used in arid climates such as Beijing. A multifunctional use of the soil filters is being tested for this purpose. This means that in dry weather, the available filter area will be used for direct treatment of surface water. This protects the plant filters from drying out and simultaneously leads to an increased cleaning effect.
The joint project is led by the Institute for Sanitary Engineering of the Leibniz University of Hannover (ISAH) and funded by the Federal Ministry of Education and Research for 3 years within the framework of the funding measure “CLIENT II – International Partnerships for Sustainable Innovations”.
Photo: Till Ermisch (AKUT) interviews Ying ZHANG from Suzhou DeHua Eco Technology Ltd. about the discharge points at the restored Hongshuanglou Channel.
Presentation: IE expo China 2021
Brochure: KEYS Show Cases 2022
In the European joint project AquaNES, various combinations of nature based and technical systems were investigated for their suitability for wastewater treatment from 2016 to 2019. The results were described in a handout for planners and operators describing such and comparable systems. The recommendations show the potentials and reasonable applications of such combinations.
The first part of the document deals with soil filters as part of combined systems and describes possible combinations with technical pre- and post-treatment. The different possible applications of constructed wetlands as primary, secondary or tertiary treatment as well as dual use for combined sewer overflows and as a tertiary treatment stage are highlighted. Important design parameters, in particular the German code of practice DWA A-262 (2017) for the dimensioning, construction and operation of constructed wetlands for municipal wastewater treatment are summarized here and combined with the results from the demonstration sites and the experience of the authors.
In the second part, the five AquaNES sites in Greece, Germany, and Great Britain, their different applications, design and operation data, and monitoring results are presented. The two Greek sites, the Antiparos and Thirasia WWTPs, are both located on tourist-oriented islands in the Aegean Sea. The solution at Antiparos focused on creating a robust, nature-based system that could handle fluctuating hydraulic and organic loads and meet the Greek standard of water reuse for irrigation. At Thirasia, a soil filter was integrated into a number of different engineering processes. Here, photocatalysis via TiO2 was also experimented with and downstream membrane filtration was tested. In Germany, an innovative retention soil filter was constructed in Rheinbach (Erftverband) for the combined use as a fourth treatment stage and for treating combined sewer overflows. At the Schönerlinde wastewater treatment plant, the combination consisted of an ozone plant and a downstream soil filter. Here, the retention of organic micropollutants such as pharmaceutical residues and metabolites in the effluent of the wastewater treatment plant was also demonstrated. Finally, the effectiveness of soil filters with reactive filter material made from blast furnace slag was investigated in long-term operation at the Packington site (UK).
Further information: Heribert Rustige
Download: Report
Mankind is facing “unprecedented suffering”, according to scientists from all over the world, if it does not seriously fight against global warming. 11,000 scientists warn against a “Continue like before”. Scientists warn that three quarters of the 184 pledges submitted to save greenhouse gases are not ambitious enough. Measured against the goal of reducing emissions by at least 40 percent by 2030, only the 28 EU states and seven other countries are on the right track (quote: ARD, Tagesschau 5.11.2019).
Already on 20 September the AKUT partners joined the call of commercial enterprises with Entrepreneurs For Future. It demands an ambitious climate protection law from the Federal Government of Germany.
However the federal government has passed a probably ineffective climate law, which will not reach the goals. We share the protest of the students of Fridays For Future.
Few days before the world’s governments meet in Madrid for the World Climate Conference, we need to reaffirm our commitment to effective climate legislation so that there are no more excuses for policy makers not to act effectively.
The Federal Government justifies its hesitant measures with the fact that it cannot impose consistent climate protection on people. However, climate protection and social policy must not be played off against each other.
For the first time, climate activists, environmental, development, social and welfare organisations are joining forces. We show: Climate protection and social justice belong together indivisibly. People in the Global South and future generations must have a climate-friendly future! A social-ecological turn is a huge chance for a fairer society – here and worldwide!
For more than 30 years AKUT has been working on technical solutions for environmental protection. We can no longer solve the global problem without a strong climate protection program also of the German government and a change of awareness among each individual.
Go out with us and with millions of people this Friday 29 November 2019 to the streets and demand effective climate protection now and for all.
Overall, the framework conditions in South Africa for the generation of electricity from sewage gas are rather difficult. The remuneration for feed-in from renewable energies is fixed at auctions, this procedure prefers scalable technologies such as photovoltaics. Biogas, on the other hand, is limited by the availability of raw materials. This restriction applies in particular to the conversion of sewage and landfill gases into electricity. The unique selling point of biogas, simple storage and power generation at peak times, is also not affected by this process of auctioning.
Thus, the only economically decisive factor on the South African energy market is the savings in own electricity consumption. The current electricity prices of around 1.20 rand/kWh (around 0.08 €/kWh) are low by German standards. However, the electricity price has multiplied since 2007: at that time, it was 0.013 €/kWh. In addition, annual price increases of 10% have been announced.
In this field of tension AKUT was commissioned by the Deutschen Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH to prepare two studies on the use of sewage gas for the two sewage treatment plants Kingstonvalle and Zeekoegat.
Economic plus ecological advantages
Against the current background of water scarcity in Cape Town, the relevance and explosive nature of the topic becomes very clear. The lack of rainfall is primarily attributed to climate change. The studies therefore identify emission reductions, in this case reductions in methane emissions, as a significant advantage in addition to economic advantages. At present, the gas produced by sewage sludge digestion is released into the atmosphere without further measures. This is now to be changed so that the gas is collected, processed and used for power generation.
The studies present detailed comparisons of various technical components, operating models and organisational forms. In both sewage treatment plants, the economic benefit can be maximised by optimising the utilisation of the existing digestion towers. Capacity utilisation is to be increased by adding so-called co-substrates, either digested sludge from neighbouring sewage treatment plants or waste from the agricultural industry. The latter could be identified by local AKUT employees so that specific modelling could be carried out, taking into account both the biogas potential and transport costs.
Economically reasonable are also the variants with an exclusive treatment of the sewage sludge of the sewage treatment plant. However, the then lower investments will lead to a slight reduction in profitability.
In addition to the technical components and the various operational management, operator models from in-house operation to BOT models were also examined. Two preference variants were determined from six different operator models.
The decision now lies in the field of politics. Should the measures be implemented? Which of the preferred variants is preferred? GIZ and AKUT are ready to continue to support the City of Tshwane and Mbombela municipalities – both in decision-making and in technical implementation.
The international IWA conference on sustainable solutions for small water and wastewater treatment systems (s2small2017) was held October 22-26 in Nantes, France. Florent Chazarenc (IMT Atlantique) chairman of the conference emphasized that small systems play a significant role in solving problems of humanity: „Small is beautiful, efficient and affordable – small is the future“ he said. More than 200 participants responded to the call and discussed their proposals for solutions in the areas of resource-oriented sewage systems, wastewater treatment and recycling.
As a German contribution to the improvement of small sewage treatment plants Heribert Rustige, AKUT partner from Berlin, presented the new DWA worksheet A 262 on the topic of constructed wetlands. This guideline is expected to be published in November 2017 and replaces the previous A 262 from 2006, whereas many new solutions and system variants have been added to the new worksheet. This includes the so-called French system, which consists of a combination with raw wastewater pre-treatment in a planted gravel filter and post-treatment in a planted sand filter (e.g. Phragmifiltre). Another newly described method using active aeration is particularly innovative. It was developed by Scott Wallace in the USA and extensively tested on site for several years in Germany by the UFZ research institute in Leipzig.
International Interest in the German Constructed Wetland Guideline
In the past, the A 262 had already attracted interest from other countries. It was last translated into Russian. Many users are now waiting for the release of the current version. An English version will also be available soon from the DWA in Hennef.
The advantage of such a detailed set of rules is the increased safety for planners and operators. The worksheet specifies minimum requirements for the dimensioning of soil filters and refers to values derived from practical experience. The user must check in each case whether the boundary conditions are correct in his application. In doing so, the regulations focus on the treatment of domestic and municipal wastewater, including combined sewerage systems. In addition, the treatment of grey water in soil filters is also taken into account.
The tables, which describe, for example, the different wastewater compositions or specific design values, are helpful. Various useful combinations of processes are shown. However, Rustige emphasized in his speech that the guideline is not a simple construction manual, as it requires specialist knowledge. No design formulas or modeling approaches are shown because they have not yet proven themselves in practice.
What is more interesting is the presentation of minimum requirements with which certain effluent values or performance degrees can be achieved. In the theoretical modeling of treatment efficiency, it is often not taken into account that hydraulics or oxygen transfer rates can be decisive limiting factors, which in the worst case can lead to a total clogging of the soil filter. It is better to orientate oneself on the statistically relevant results derived from practice, as they are used in the A 262.
Final workshop on rainwater harvesting in South Morocco
A circular path has been completed in order to present measures for strengthening the agricultural sector in the region Souss-Massa-Draâ in December 2015. Rainfalls are less frequent and single events often heavier in these oases that are highly affected by climate change.
Due to poor and infrequent water supply traditional agricultural activities have declined significantly and heavy rainfall events are cause of erosion in many areas. A combination of various decentralized and small-scale measures was set up to improve the situation. One example is the construction of several ground sills / small dams that have been built in the long branched valleys above the oasis Tidrheste to reduce erosion.
Water retention measures increase the infiltration rate and usable water is directed into small channels. As a result of the collection of water in Negarim microcatchments and decentralized cisterns the olive tree cultivation is now possible without usage of (scarce) groundwater.
The successful international cooperation of AKUT Umweltschutz Ingenieure Burkard und Partner, Schulze-Matthes Ingenieure, the Association Ennacer de Développement (AED) of Tidrheste and the GIZ shall be continued. Further information about the project, irrigation, erosion protection and Rainwater Harvesting in arid climate zones may be obtained from Heribert Rustige.