3.3.1. TPS System at the TerraBoGa Project
The main objectives of the TPS system at the TerraBoGa project [
28] are to manage, as effectively and efficiently as possible, the organic resources and nutrients from the garden as well as from a public toilet facility. Organics and nutrients have to be managed according to the principles of closed loop recycling economy, while also addressing energy aspects related to organic waste. The project is connected to both the urban sewer system and the centralized drinking water supply. Only wastewater from toilets is processed with the aim of reusing as much as possible the contained solids and nutrients in the TPS system. The greywater from washbasins and the remaining liquid from wastewater treatment are discharged in the urban sewer system and hence are not reused. In line with this, the urine, organic solids, and nutrients from the blackwater are used for TP production. The TP is applied in horticulture and/or agriculture at the neighborhood level within the botanical gardens.
This alternative TPS system consists of the following main components (
Figure 3). Blackwater from water saving toilets is to be separated into a liquid and a solid phase using a wedge wire filter. The solid phase, consisting of feces and toilet paper, is stored in a plastic barrel, the bottom of which contains approximately 10 L of Bio-Char enriched with EMs. After the barrel is filled to its maximum level, the feces and toilet paper are finally covered with another 10 L of Bio-Char enriched with EMs, before the barrel is sealed airtight and replaced with en empty barrel.
Figure 3.
Flowchart of TPS System of the TerraBoGa project, illustrating the connections between processes and/ or technologies (in boxes) and resulting products (without boxes). All processes except the steps after the discharge of grey water and liquids in the sewer system occur within the botanic garden.
Figure 3.
Flowchart of TPS System of the TerraBoGa project, illustrating the connections between processes and/ or technologies (in boxes) and resulting products (without boxes). All processes except the steps after the discharge of grey water and liquids in the sewer system occur within the botanic garden.
The liquid phase is transported through a so-called “charcoal nutrients activator”, a container filled with charcoal that absorbs as much of the dissolved nutrients and micro pollutants as possible. All components are located in an underground chamber next to the public toilet facility to facilitate the discharge of filtered blackwater due to free flow to the public sewer. An opening at the top of the chamber facilitates the removal and exchange of the barrel with pre-fermented solids and the charcoal loaded with nutrients. The Bio-Char is produced using pyrolysis in a “carbonizer” from woodchips, which are waste products from plants growing in the botanic garden. The resulting heat, a byproduct from the pyrolysis process, is used for district heating within the botanic garden. The EMs are produced externally. To meet sustainability criteria, all products should be transported using emission free transport [
1,
5,
20,
28].
Urine from waterless urinals is collected in “bag-in-box” containers in the public toilet facility. The collected urine is transported regularly using emission free transport for the production of fertile soil to a location within the botanic garden. The soil production incorporates urine, pre-fermented organic solids, nutrient activated charcoal from the blackwater treatment process, and biomass resulting from the operation of the botanic garden. The resulting TP is applied within the botanical gardens at a neighborhood level in horticulture and/or agriculture.
3.3.2. Background and Resource Flows of the TerraBoGa TPS System
The aims of the TerraBoGa project are the optimal management of material flows to achieve higher resource efficiency through the optimization and redesign of the original organic waste management and sanitation systems. Furthermore, the project aims for the creation of added ecological, economical, and social values for the botanical gardens.
The TPS system of the TerraBoGa project is based on an integrated zero-emission approach. The goal is the realization of a closed loop recycling system for organic materials within the botanic garden. Energy aspects, such as energy efficiency and renewable energy production and utilization, are also addressed. However, both the disposal of organic wastes from the botanic garden as well as the provision of fertilizer and soil for the botanical gardens was originally managed by external service providers. Both disposal and provision were based on a fee system, representing a financial burden on the management of the botanic garden. In order to avoid financial loss and to generate additional values, a closed loop resource management system was designed with the aim of producing organic waste, fertilizer, and soil. The expensive external service provision system was replaced by liquid and solid organic waste processing systems. The function of the system is the local production of fertile black soil and TP, the on-site generation of Bio-Char and district heat, and the operation of the botanic garden itself.
The TerraBoGa project design and setup is fundamentally based on a resource flow analysis. The considered flows include 750 m3 of green garden wastes and approximately 230 m3 of long grass clippings per year. Also included are the organic wastes and nutrients from visitors and staff, which are generally left at the Botanical Garden Berlin in the form of excreta and discharged to the urban sewer system. In addition to the material recycling potential, analysis was also carried out on how the TerraBoGa project could contribute to a CO2 neutral energy supply by using renewable fuels in the form of biomass.
Based on the results from the resource flow analysis, a combined heat and charcoal generator was commissioned and installed at the Botanical Garden Berlin, and started operation in October 2013. The working principle of the facility is that of pyrolysis as it produces fewer emissions than conventional combustion or charcoal burning systems. The Bio-Char is used thereafter for the pre-fermentation and filtration processes as well as for the production of TP. The generated heat is used for district heating at the neighborhood level for the buildings in the botanical gardens.
The TerraBoGa TPS system is also based on an integrated system approach. Addressed are the utilization of nutrients and organics from blackwater and urine for the production of fertile soil, and the sustainable use of other resources, particularly water. Efficient water use is realized by replacing old flush toilets and urinals with waterless urinals and water saving toilets. It is important to highlight that if such urinals and toilets were to be installed in all toilet facilities in the botanical gardens, approximately 2300 m3 of drinking water could be saved per year, while the production of the same quantity of wastewater could be avoided. A financial calculation considering the fees for drinking water and wastewater revealed that, as of June 2014, about 5 Euros per m3 (approximately 11,000 Euro) in drinking water and sewage fees could be saved annually.
Unfortunately, not all of the sanitation facilities in the TerraBoGa project could be remodeled. The conventional toilets and urinals were only replaced in some selected sanitation facilities for employees and visitors to the garden. In the sanitary facility for the gardeners, four toilets were replaced with water saving “GreenGain” [
30] flush toilets (see
Section 3.3.3 for detailed technology description). In the most frequented public toilet facility for visitors to the botanic garden, three flush urinals were replaced with waterless urinals (see
Section 3.3.3, “
Technology Description of the TerraBoGa TPS System” for detailed technology description). Furthermore, seven of the conventional flush toilets were replaced with seven water saving toilets in the same facility.
However, by installing water saving toilets and urinals it could also be successfully demonstrated that added values can be generated through the saving of resources and related savings in drinking water and sewage fees. Notwithstanding, the installation of water saving toilets and waterless urinals is only the first basic step to facilitate the separated collection of wastewater streams and the recycling of valuable ingredients such as organic material and nutrients.
The urine in the system is collected from waterless urinals by free flow in new and innovative non-ventilated bag-in-box containers [
31] (see
Section 3.3.3 for detailed technology description) to avoid nitrogen losses due to evaporation [
32,
33]. For further processing, the urine is discharged by free flow in movable plastic casks. The full casks are then transported to the composting facility of the botanic garden, where Bio-Char gravel is saturated with the urine to absorb and bond the contained nutrients. The urine activated Bio-Char is used at the same location and together with other ingredients for the production of TP.
The separation of solids from the blackwater originating from water saving toilets was first undertaken using a wedge wire filter, which was replaced with a spiral strainer in August 2013 (see
Section 3.3.3 for detailed description of technology). The blackwater is transported by free flow through the strainer, which separates the liquid from the solid phase, which consists of feces and toilet paper, and is discharged in plastic barrels with a capacity of 60 L. The empty casks are filled with approximately 10 L of Bio-Char mixed with lactic acid producing EMs before they are connected to the separation system. The mixture of Bio-Char and EMs facilitates a proper pre-fermentation process of solids discharged in the barrel and avoids methane formation. When a cask is filled to 90%, the content is covered with another 10 L of the Bio-Char and EMs mixture before the cask is closed with a lid. Airtight sealing of the filled barrels is crucial to facilitate a proper lactic acid fermentation process.
The liquid phase, originating from the spiral strainer, is almost free of solids, but is rich in nutrients. To facilitate the separation of nutrients from the filtered blackwater, HATI GmbH plans to develop a Bio-Char filter, a so-called “charcoal nutrient activator”. The aim of the filter is to absorb the nutrients from the liquid phase before it is discharged by free flow into the urban sewer system.
According to intermediate project results and calculations, the TPS system can be used to recover the following resources from the installed toilets and urinals in the present design of the TerraBoGa system in the Botanical Garden Berlin:
Nitrogen: 65 kg/a
Phosphorous: 8 kg/a
Urine: 10 m3/a
However, if all toilet facilities for employees and visitors are remodeled and equipped with the TPS system, the amount of total resources that could be recovered from the installed toilets and urinals is largely improved:
Nitrogen: 1.613 kg/a
Phosphate 164 kg/a
Urine: 211 m3/a
After proper lactic acid fermentation, the nutrient rich Bio-Char, EMs, and feces mixture is used together with collected urine, charcoal, green garden wastes and grass clippings for the production of fertile black soil. In order to facilitate proper humification, the mixture has to undergo further fermentation and composting processes. The majority of this TP substrate produced in the Botanical Garden Berlin is used within the gardens for growing shrubs and flowering plants. Part of the TP is also used to grow fast growing timber (e.g., poplar, willow, paulownia tree), which can potentially be used as energy crops and for the production of Bio-Char.
Fast growing timber can be continuously harvested after an initial growing period of 4–5 years. The harvested timber is shredded and dried together with the cut copse and stem wood before it is further processed for the combined generation of charcoal and heat in a carbonization plant (see
Section 3.3.3 for a detailed description of technology), which was commissioned and installed in the framework of the TerraBoGa research project. The aim of the TerraBoGa project is the continuous and unlimited operation of the TPS system and the carbonization plant, beyond the limited research project period of approximately 5 years. Therefore, the carbonization plant, the so-called “charcoal producing woodchip boiler” (CPWB) has been designed for the sustainable and efficient processing of biomass in the form of wood materials from the botanical gardens. The CPWB has a production rate capacity of 13 kg/h Bio-Char per 40 kg/h of woodchips with a 60 kW rated heat capacity. The produced heat is distributed via the water born district-heating network and used throughout the year for the heating of water and a neighboring paint shop.
The CO2 emitted during the operation of conventional woodchip boilers is equal to the amount of CO2 absorbed by the biomass during the growth process. Accordingly, the burning of biomass is a CO2-neutral process. In contrast, during the operation of the “charcoal producing woodchips boiler”, only the hydrogen contained in the biomass is used for the production of thermal energy where the chemically stable carbon is transformed to charcoal (Bio-Char). One kilogram of pure charcoal binds 3.6 kg of CO2. Taking into account all of the wooden biomass from the botanical gardens that could be processed in the CPWB, approximately 70 t/a of CO2 could be permanently stored in the TP that is produced and used in the botanical gardens.
The financial funding of the TerraBoGa R&D project by German Federal Ministry of Education and Research (German: BMBF - Bundesministerium für Bildung und Forschung) is limited to June 2015 [
28]. However, the aim of the CPWB and the complete applied TPS system, operated and evaluated in the framework of the TerraBoGa research project, is to contribute permanently to the efficient and sustainable use of renewable resources in the Botanical Garden Berlin. Furthermore, the aim of the project is to stimulate further development of TPS systems.
3.3.3. Technology Description of the TerraBoGa TPS System
This section presents the specific technologies applied in the TPS systems considered in this paper.
Water saving toilets: Commercially available flush toilets or water closets generally use at least 6 liters of water per full flush, or even more. In contrast, the Omnia GreenGain toilet [
30] (
Figure 4), applied in the TerraBoGa project, only uses 3.5 liters per full flush (feces) and only 2 liters per half flush (urine). Due to the specific working principle with improved hydraulic properties, the toilet has very good flush and cleaning properties, even though the water consumption is comparably small. Due to the small water demand, additional savings can be achieved by using components with smaller dimensions in the systems for water supply and wastewater management.
Figure 4.
Omnia GreenGain toilet [
30].
Figure 4.
Omnia GreenGain toilet [
30].
Blackwater treatment: Blackwater consists of a mixture of feces, urine, toilet paper, and flush water. For the separation of solids and liquids in blackwater, a separator consisting of a wedge wire filter is connected to the water saving flush toilets. An integrated spiral conveyor connected to the filter transports the separated solids to a storage tank (plastic barrel/cask) where they are mixed with Bio-Char and EMs.
Figure 5 illustrates the main components of the blackwater separator.
Figure 5.
Separator consisting of a wedge wire filter and spiral conveyor for the separation of liquids and solids [
34]. The main components are: 1. Black water inflow; 2. Separator; 3. Cask for solid material (Bio-Char, feces, toilet paper); 4. Outlet of the liquid phase.
Figure 5.
Separator consisting of a wedge wire filter and spiral conveyor for the separation of liquids and solids [
34]. The main components are: 1. Black water inflow; 2. Separator; 3. Cask for solid material (Bio-Char, feces, toilet paper); 4. Outlet of the liquid phase.
Waterless urinals: Many of the waterless urinals available on the market have odor traps, which are filled with liquids, allowing the urine to pass through while closing airtight, and thus trapping odor from the drainage system. In contrast, the waterless Centaurus [
35] urinals (
Figure 6) installed in the TerraBoGa project have odor traps that are based on a mechanical working principle. A special rubber siphon trap allows the urine to pass through but closes airtight and thus traps odor from the drainage system. No chemicals, no electricity, and no water are required for proper operation.
Figure 6.
Centaurus waterless urinals and the special rubber siphon trap [
35].
Figure 6.
Centaurus waterless urinals and the special rubber siphon trap [
35].
Urine collection in “bag-in-box” system: The urine from the waterless urinal is collected by free flow in a small container from where it is pumped into the flexible and non-ventilated bag-in-box container. This container, also known as an ‘inliner’, unfolds automatically when it is filled and folds in automatically when it is emptied. Accordingly, the contained fluid is independent from the filling level of the container that is always covered by the synthetic tank material and not exposed to air. The advantage of this container type is that nitrogen loss from the urine by evaporation can be effectively avoided. For transport and further processing to TP, the urine is discharged by free gravity flow from the bag-in-box tank with a capacity of 250 L to movable plastic casks with a capacity of 60 L (
Figure 7).
Figure 7.
Urine collection system, including waterless urinals, supply container, bag-in-box container (flexible intermediate bulk container) and barrel for the transport of urine.
Figure 7.
Urine collection system, including waterless urinals, supply container, bag-in-box container (flexible intermediate bulk container) and barrel for the transport of urine.
Carbonization of wood chips: The carbonization of wooden biomass represents a promising technology, as it is effective in carbon dioxide free renewable energy production. Carbonization is safe, energy-effective, environment-friendly, and can contribute significantly to carbon dioxide storage. The ‘charcoal producing woodchips boiler’ installed in the framework of the TerraBoGa research project is a Biomacon biomass converter [
36] (
Figure 8). This technology can generate from 40 kg of woodchips, 13 kg of Bio-Char, and with a 60 kW rated heat capacity per hour. Resources required for operation and application of generated products are found within the botanical gardens.
Figure 8.
Biomacon biomass converter [
36] applied in the TerraBoGa research project.
Figure 8.
Biomacon biomass converter [
36] applied in the TerraBoGa research project.