Wetlands for wastewater treatment sludge
BE CIRCULAR, BE EFFECTIVE: STOP SENDING SLUDGE TO THE LANDFILL
Wetlands for wastewater treatment sludge
BE CIRCULAR, BE EFFECTIVE: STOP SENDING SLUDGE TO THE LANDFILL
Wetlands for wastewater treatment sludge
BE CIRCULAR, BE EFFECTIVE: STOP SENDING SLUDGE TO THE LANDFILL
WETLANDS COURSES
QUESTIONS
Frequent
Wetland systems can be technically classified as planted, percolating, and/or submerged biological filters with very low loading rates for attached biomass. The mechanisms of organic matter degradation and nutrient removal are governed by the microbiota that colonizes and adheres to the system bed (support medium and root zone) and meet the technical/scientific principles of sanitary microbiology, just like classic biological reactors. The design criteria and mechanisms for removing organic matter and nutrients in wetland systems follow the same sanitary engineering concepts as other biological systems with attached biomass, fundamentally dimensioned by the hydraulic application rate and organic loading rate.
Constructed wetlands technology is a well-established, publicly available technology worldwide, applicable to various fields, from municipal sewage treatment to biological sludge and complex industrial and mining wastewater. Early research involving this technology began in the 1960s with Dr. Käthe Seidel (1907-1990), a limnologist biologist at the Max Planck Institute, who demonstrated the potential of vegetation in lentic environments to degrade various compounds. With advancements in research, new criteria and disciplines were incorporated into the embryonic concept, making its applicability viable as a sanitary engineering solution for the treatment of sewage, water, and sludge, in the manner now established worldwide.
Today , the technology is widely disseminated and consolidated, based on sound engineering criteria. The technology is endorsed by renowned entities such as the IWA (International Water Association), UN Water (UN), EPA (Environmental Protection Agency USA), European Environment Agency, and others. To access reliable information about wetland technology, operating principles, sizing, advantages, and limitations, access the "13 books" acclaimed by the national and international community on the subject, listed on our blog:
No. As has been established in all scientific studies on the subject, it should be emphasized that it is not the vegetation that treats the effluents in constructed wetland systems.
Wetland systems can be technically classified as percolating and/or submerged biological filters with very low loads on attached biomass. The mechanisms of organic matter degradation and nutrient removal are governed by the microbiota that colonizes and adheres to the system bed (support medium and root zone) and meet the technical/scientific principles of sanitary microbiology, just like classic biological reactors with attached biomass.
Plants are autotrophic organisms that synthesize their own food (photosynthesis), and for this reason they do NOT consume organic matter. Regarding nutrient removal (especially nitrogen and phosphorus), the loads applied in wetland systems, a product of the hydraulic application rate and the concentration in the raw sewage, are 50 to 100 times greater than the nutritional demand of the plants. Therefore, on average, even plants with high growth/productivity rates (forage grasses, for example) consume less than 2% of the supplied nutritional load. The design criteria and mechanisms for removing organic matter and nutrients in wetland systems follow the same sanitary engineering concepts (classical microbiology) as other biological filters with attached biomass, fundamentally dimensioned by the hydraulic application rate and organic loading.
Therefore, the answer is clear: it is not the plants that treat sewage. And therefore, it is not necessary to prune the vegetation in order to guarantee the efficiency of the system! Wetland systems remove organic matter, remove nitrogen and can, in special configurations, remove phosphorus, just like other classic biological systems, but the plants are not primarily responsible for this.
To access reliable information about wetland technology, operating principles, sizing, advantages, and limitations, please visit the "13 books" acclaimed by the national and international community on the subject, listed on our blog:
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But then what is the role of vegetation? For reflections on these and many other questions, access the article by clicking on the link below:
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Constructed wetlands can receive raw sewage, biodegradable industrial effluents, biological sludge, and inorganic water. For each type of water, sludge, and effluent, there are specific engineering criteria and wetland layouts that can be combined. Understanding the applicability, operating principles, and sizing of each typology is what defines the success of the solution. Regarding the diversity of layouts, there is a post on our blog that addresses this topic ( click here to access).
Among the commonly used types, vertical flow wetlands are the only ones suitable for receiving raw sewage. In France, a large part of the more than 4000 plants implemented, using constructed wetland technology, receive municipal raw sewage and meet discharge standards with BOD below 25 mg/L and 100% removal of ammoniacal nitrogen ( click here to read more about the efficiency of the systems ). On the other hand, horizontal wetlands are not designed to receive raw sewage, being used for secondary effluent treatment. Obviously, wetland wastewater treatment plants for sanitary sewage, like any wastewater treatment plant, require good preliminary treatment (screening and/or sieving to remove coarse solids and structures to remove excess oils and greases).
For sludge treatment, UGL Wetlands only accept sludge that has already undergone primary digestion of organic matter, ensuring that the volatile solids-to-total solids ratio is less than 65%, typical of stabilized sludge. For these reasons, it is always important to have a good characterization of the sludge to be treated, an essential factor for the successful operation of any technological arrangement. Another important point is that the characteristics of the sludge directly influence the application rates and the areas required by the system. Just like wetlands for treating effluents, UGL Wetlands can be designed to receive any sludge flow rate. The largest wetland in the world, for treating wastewater treatment plant sludge, serves a population of over 1.5 million inhabitants (To learn more about these cases, click here ). Therefore, the limitation of wetlands is not in the flow rate, but in the area requirements and the costs and availability of land.
Do wetlands used for treating sanitary wastewater and sludge generate odor? Do they attract mosquitoes?
Like aerobic technologies, constructed wetland systems, whether for sludge dewatering and mineralization or sewage treatment, do not produce unpleasant odors. This is guaranteed by the fact that they are extensive and aerobic treatment systems with relatively low loading rates, which prevents the creation of anaerobic environments in the beds. Preserving the predominantly aerobic condition, there is no generation of H2S (hydrogen sulfide) into the air, which, as mentioned, is the main cause of unpleasant odors. In an aerobic environment, this compound is oxidized to SO43- (sulfate), which is non-volatile. Therefore, it is possible to implement wetland systems very close to residential areas. In some technological arrangements, it is possible to integrate the system with a square or park, creating a harmonious environment for coexistence and environmental education.
The types of wetlands used by the company Constructed Wetlands for sanitary sewage treatment, vertical and/or horizontal wetlands, do not attract mosquitoes because there is no visible water surface, and consequently no environment for proliferation. In these types, unlike surface wetlands, the effluent flow occurs subsurface, that is, below the bed of stones. The system also operates at a low load and there is no accumulation of large quantities of organic material on the surface of the bed, so the attraction of flies is greatly reduced.
What are the area requirements for implementing wetland systems for sanitary wastewater and sludge?
Constructed wetlands are passive and extensive treatment systems. Unlike intensified treatment plants, they do not use chemicals or electromechanical elements in their reactors. On the other hand, as a condition, wetlands, in resonance with other extensive technologies, occupy larger implementation areas. For this reason, the availability of land is a prerequisite for enabling the implementation of the technology. Although the dimensions of wetlands are related to design criteria (according to the effluent characterization and treatment objectives), as an estimate, 0.8 to 2 m² are needed for every 160 liters of daily flow (corresponding, on average, to the sewage production of 1 inhabitant). It is also necessary to provide an additional 50% to 80% of area for surrounding areas (access roads, support structures, preliminary treatment, etc.).
For sludge wetlands, although dimensions are also related to design criteria (according to sludge characterization and locational aspects), as an estimate, between 0.10 and 0.45 m² are needed for every 17.5 kg of TSS/year (corresponding, on average, to the dry sludge production of 1 inhabitant per year). It is also necessary to provide an additional 50% to 80% of area for surrounding areas (access roads, support structures, equalization tank, preliminary treatment, etc.).
We know that wastewater or industrial effluent treatment processes emit greenhouse gases (CO2 and CH4) to varying degrees. However, anaerobic treatment processes, such as anaerobic lagoons, septic tanks, UASB reactors, and anaerobic filters – the latter two widely used in compact wastewater treatment plants – generate up to 80 times more methane than aerobic processes – such as activated sludge, aerated biofilters, biodisks, and constructed wetlands. Based on a study published in the Ibero-American Journal of Environmental Sciences ( link to access the article ), prepared by our team in partnership with researchers from UFMG and UFSC, we simulated the GHG emission values of constructed wetlands compared to other treatment technologies. The calculations are performed in light of the greenhouse gas inventory guidelines of the Intergovernmental Panel on Climate Change – IPCC. To read more about this subject, click here.
According to the same study, on a national scale, incorporating constructed wetlands into the sanitation technology matrix could reduce total methane emissions from wastewater treatment in Brazil by more than 10%, a figure that represents approximately 867 million tons of carbon dioxide equivalent that are no longer emitted annually. In carbon credits, this reduction represents an average revenue of about 35 million dollars per year!
For calculations of GHG emissions, we also suggest reading our blog article on the subject:
The answer to this question is documented in the thousands of systems deployed around the world and demonstrated in international scientific literature. Therefore, to answer this question, nothing is better than presenting data. In one of the landmark articles on the subject, the team of Dr. Pascal Molle, one of the world's leading researchers in the field of constructed wetlands, evaluated the performance of 3,500 constructed wetland systems deployed in small communities in France using a 30-year database.
The systems evaluated were the classic French arrangement with two treatment stages. The first set of tanks has three parallel beds and receives raw sewage with the aim of retaining suspended solids and removing BOD and COD. The second set of tanks has two parallel beds, which receive the effluents from the first set and aim at advanced removal of BOD and COD and complete nitrification.
From the 3,500 stations in the database, the authors selected 415 arrangements with two-stage vertical flow wetlands and evaluated the efficiencies of both the first stage and both stages. The values reveal a removal efficiency of 83% for TSS and 77% for COD in the first stage alone. The two-stage arrangement showed high removal rates, reaching 87% for COD, 93% for TSS, and 84% for TKN.
The concentrations achieved by the single-stage arrangement of COD, BOD, and TSS suggested that in regions with warmer (tropical) climatic conditions, it would be possible to adopt only one treatment stage, reducing the area required for the stations.
When the goal is to achieve complete nitrification and advanced BOD and COD removal, the second stage of the French system performs fantastically. It's no wonder it has become the standard solution for small communities in France!
To access the publication mentioned above and other relevant publications that demonstrate the efficiency of wetland systems around the world, please visit our article:
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