Sludge Treatment Reed Bed Systems Research Articles

Combined treatment of sludge from a wastewater treatment plant and wastewater from a stormwater basin in a Sludge Treatment Reed Bed System during >25 years

A review of treatment of stormwater and dewatering of sludge in a Sludge Treatment Reed Bed system (STRB) during operation and emptying of the basins over >25 years of operation. Kallerup Wastewater Treatment Plant (WWTP) was designed with mechanical, biological, and chemical treatment including nitrification and denitrification and since 2009, the sludge production has stabilized to 160–200 tons DS yr−1, which resulted in an area load of 24.7–40.9 kg DS m−2 yr−1. Four-to-six-time yearly wastewater has been pumped from the stormwater basin to the STRB system representing volumes in the order of magnitude that corresponds to 64–383 loads of 70 m3. During the operation period (2003−2022), approximately up to 1.40 m of sludge residue, equivalent to an accumulation rate of 0.06–0.10 m yr−1, had accumulated in the basins. During the operation period 2012–2016, the maximum runoff rates have been very stable with maximum runoff rates of up to 0.018–0.024 l sec−1 m−2 and 0.011–0.024 l sec−1 m−2 for the first and last batch, respectively.

Assessment of diversity and composition of bacterial community in sludge treatment reed bed systems

Due to their low emission of odours and lack of the need to apply additional chemical agents, sludge treatment reed beds (STRBs) constitute an economically feasible and eco-friendly approach to sewage sludge management. Correctly designed and operated STRBs ensure effective reduction of the dry matter content coupled with the mineralisation of organic compounds. Successful operation of STRBs relies on complex interactions between the plants and microorganisms responsible for the decomposition of organic matter and nutrient cycling. While the biocenoses of wetland systems dedicated to wastewater treatment have been intensively investigated, in the case of sludge treatment applications, there is a deficit of available microbial data. The aim of this study was to explore the diversity and spatial distribution of the bacteria in three distinct STRBs which differ in maturation and feeding patterns. Analyses of the dry mass and organic matter content showed the general trend of the sludge stabilisation processes advancing through the bed depth, with the best performance in the Matured Continuous Feed (MCF) bed being noted. Samples from the MCF bed showed the statistically greatest biodiversity in relation to the other beds. Moreover, increased biodiversity of microorganisms was observed on the surface of the STRBs and the bottom zone of the MCF equipped with a passive aeration system, which proves the application of such solutions in order to enhance the performance of the process. The results of 16S rRNA gene sequencing revealed that Bacteroidetes, Proteobacteria and Firmicutes contributed approximately 80% of all identified sequences read. Network analysis revealed dominant role of Bacteroidetes in the formation of interspecies co-existence patterns. Nitrospira was the most abundant organism responsible for nitrogen metabolism in the STRBs.

Bacterial community composition and diversity uncovered in experimental sludge treatment reed bed systems with different swine slurry hydraulic loadings

Nowadays swine slurry management is a very important environmental issue. Sludge treatment reed bed systems are sludge treatment systems based on constructed wetlands.The present study characterizes via 16S rRNA gene high-throughput the bacterial communities contained in untreated swine slurry and treated swine slurry by means of mesocosm-scale sludge treatment reed beds receiving different slurry loadings.The bacterial community composition varied between the treated and untreated slurry, with a notable slurry loading influence also observed. Richness, diversity and ordination measurements of the studied communities evidenced profound differences between the untreated and treated swine slurry bacterial communities; and only slight differences among the treated swine slurry communities. Interestingly, the slurry loading allowed to define two groups: mesocosm communities residing in the highest hydraulic slurry loadings and other mesocosm communities. The pH value emerged as an important community composition, diversity and ordination predictor.The functional bacterial community composition was predicted through the in silico approach. Results confirmed that the main nitrogen cycle metabolic pathways were present in the mesocosm communities with ammonification and assimilatory nitrate reduction as the most commonly detected nitrogen pathways in treated swine slurry.

Life cycle assessment comparing the treatment of surplus activated sludge in a sludge treatment reed bed system with mechanical treatment on centrifuge

Abstract In Denmark, the conventional method for treating sewage sludge is mechanical dewatering and subsequent storage. However, sludge treatment reed bed systems, which are holistic sludge treatment facilities combining the dewatering, mineralisation and storage of sludge, have been more common during the last three decades. Treatment of sludge in a sludge treatment reed bed system can be combined with post-treatment (further dewatering and mineralisation) on a stockpile area. This study aimed to compare the environmental performances of a mechanical sludge treatment method with the sludge treatment reed bed system strategy, using the life cycle assessment approach and a life cycle inventory based on newly generated data obtained from Danish reference facilities. The scenarios based on the different treatment methods were initiated by sludge entering the sludge treatment reed bed system or the centrifuge and terminated by land application of the final sludge product. The environmental impacts caused by the sludge treatment reed bed system strategy were comparable to or lower than those caused by the mechanical sludge treatment method. The impacts on climate change were the same for all the treatment scenarios; however, the conversion of organic carbon and nitrogen into gas species was more efficient in the sludge treatment reed bed system compared to mechanical treatment. Thus, mechanically treated sludge contained more nitrogen, causing higher nitrogen emissions (nitrous oxide, nitrate and ammonia) when applied on land. Furthermore, the impact of resource depletion was higher for mechanical dewatering due to a larger fossil fuel demand related to daily operation and longer transportation distances in this scenario. According to the results of the life cycle assessment, there were no considerable environmental gains made by combining the treatment of sludge in a sludge treatment reed bed system with post-treatment on a stockpile area. However, some practical aspects, which are not expressed in a life cycle assessment, should also be taken into consideration when evaluating the performances of sludge treatment scenarios.

Nitrogen mineralisation and greenhouse gas emission from the soil application of sludge from reed bed mineralisation systems

A sludge treatment reed bed system (STRB) is a technology used for dewatering and stabilising sewage sludge via assisted biological mineralisation, which creates a sludge residue suitable for use as fertiliser on agricultural land. We evaluated the effect of sludge residue storage time (stabilisation time) for three STRBs on soil N mineralisation and CO2 and N2O emissions in soil. The experiment revealed that the N mineralisation rate and emissions of CO2 and N2O decreased as a function of treatment time in the STRBs. Mixed sludge residue (sludge residue subjected to different treatment times) for the three STRBs resulted in N mineralisation rates similar to the sludge residue subjected to a shorter treatment time but lower N2O emissions similar to the values of the older sludge residue. This finding reveals that combining fresh and more stabilised sludge residue ensures high N availability and reduces N2O emissions when applied to land.

Greenhouse gas emissions from the mineralisation process in a Sludge Treatment Reed Bed system: Seasonal variation and environmental impact

Greenhouse gas emission data from the mineralisation process in Sludge Treatment Reed Bed systems (STRB) are scarce. The aim of this study was to quantify the emission rates of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and to investigate seasonal variations in order to estimate the annual greenhouse gas emission rate of the mineralisation process. The full-scale STRB at Helsinge wastewater treatment plant (WWTP) in Denmark was chosen as the study site. Gas emission rates were measured using static surface flux chambers. The measurements were carried out in October/November 2014, March/April 2015, June/July 2015 and January/February 2016. We found that the emission rates of all included gas species were significantly affected by season. For CO2 and CH4, the highest emission rates were recorded in summer, being138 and 5.2gm−2d−1, respectively, while the lowest rates were recorded in winter, being 442 and 0.7gm−2d−1, respectively. For N2O, the highest and lowest rates were recorded in autumn and spring, being 0.47 and 0.31gm−2d−1, respectively. Emissions of CO2 and CH4 appeared to be affected by changes in temperature, while N2O appeared to be affected not only by temperature, but also by the amount of precipitation. An annual greenhouse gas emission rate (given in CO2 equivalents) of the mineralisation process was calculated for two scenarios based on the assumptions; 1) gas emission rates are not affected by the amount of sludge accumulated in the STRB and 2) gas emission rates are affected by the amount of sludge accumulated in the STRB. The results revealed that the annual global warming potential is to be found in a range between 7 and 13.4kg CO2-eq·PE−1y−1.

Sewage sludge and waterworks sludge stabilization in sludge treatment reed bed systems.

In this study, results about sludge stabilization in sludge treatment reed bed (STRB) systems in two different systems, Hanningfield STRB 1 (England), treating waterworks sludge, and Stenlille STRB 2 (Denmark), treating surplus activated sludge, are presented. The study mainly focused on the effectiveness of the STRBs systems in stabilizing sludge organic matter; in fact, parameters correlated to biochemical and chemico-structural properties of organic sludge matter were determined. Dewatering and sludge stabilization were effective in both STRBs, as highlighted by total and volatile dry solids trend. β-glucosidase, phosphatase, arylsulphatase, leucine amino-peptidase and butyrate esterase activities, enzymes related to C, P, S, N and overall microbial activity, respectively, significantly declined along the profile in both STRBs. The determination of humic carbon highlighted the formation of a stable nucleus of humified organic matter in both STRBs in the deepest layers, thus meaning the successful stabilization of sludge organic matter for both kind of sludges. Similar conclusions can be drawn from pyrolysis gas chromatography analysis (Py-GC), which enables the characterization of soil organic matter quality from a chemical-structural point of view. The pyrolytic indices of mineralization and humification showed that in both STRBs the sludge organic matter is well stabilized.

Operational strategy, economic and environmental performance of sludge treatment reed bed systems - based on 28 years of experience.

Sludge treatment reed bed (STRB) systems have been used for dewatering and mineralisation of sludge in Europe since 1988. STRB systems provide substantial environmental, economic, and operational benefits compared to mechanical sludge dewatering solutions such as belt presses and centrifuges. They require less energy, no chemicals, reduce the sludge volume and produce bio solids with dry solid contents up to 20-40% under Danish climate conditions, depending on the sludge quality. Experience has shown that sludge treated in STRBs represents a high quality product with a low content of pathogens and hazardous organic compounds, qualities that make it suitable for recycling on agricultural land. The upfront capital cost for STRBs are often higher compared to mechanical dewatering devices. However, the operational expenses (OPEX) (including energy, chemicals, bio solid handling) are significantly lower compared to conventional mechanical dewatering devices, delivering an economic break-even of about 3-5 years. This paper provides an overview of the operation and maintenance costs and environmental benefits of a typical STRB based on the experiences gained from the operation of a large number of STRBs with yearly treatment capacities between 100 and 3,000 tonnes of dry solid up to approximately 250,000 PE in Denmark and Europe.

Feasibility study of faecal sludge treatment by constructed wetlands in Sahelian context: Experiments with Oryza longistaminata and Sporobolus pyramidalis species in Ouagadougou

In Urban areas of Burkina Faso, there are essentially on-site sanitation systems, constituted of latrines and septic tanks. Faecal sludge produced by these utilities are actually rarely treated and just spilt in the environment. So, there is a need to develop sustainable treatment solutions, to preserve local populations health, water resources and environment. In order to investigate rustic sludge treatment, 12 experimental sludge treatment reed bed systems, planted with two local species: Oryza longistaminata (OL) and Sporobolus pyramidalis (SP), were constructed and monitored in Ouagadougou, Burkina Faso. The goal was to assess the potential of OL and SP planted beds to treat fecal sludge in Sahelian climate. A hydraulic load of 20–26cm/week corresponding to 15.8–21.1kg TSS/m2/year (62.6–83.5kgDM/m2/year) was applied on all the beds for 120 days. The characterization of raw fecal sludge was assessed using physicochemical parameters (DM, TSS, NO3−-N, NO2−-N, NH4+-N, PO43−-P, TP, and COD). Allometric parameters of plants on each bed were also monitored. The high contents of COD, nutrients and salinity could be particularly associated with the plants wilting and death, especially for OL. The threshold values of 1900mg/L for COD, 174.5mg/L for NH4+, 19.9mg/L for PO43− and 4400mS/cm for conductivity induced sensitive variation of plant behaviors were highlighted for Oryza longistaminata.

Musk fragrances, DEHP and heavy metals in a 20 years old sludge treatment reed bed system

The Sludge Treatment Reed Bed (STRB) technology is a cost-efficient and environmentally friendly technology to dewater and mineralize surplus sludge from conventional wastewater treatment systems. Primary and secondary liquid sludge is loaded onto the surface of the bed over several years, where it is dewatered, mineralized and turned into a biosolid with a high dry matter content for use as an organic fertilizer on agricultural land. We analysed the concentrations of five organic micropollutants (galaxolide, tonalide, cashmeran, celestolide and DEHP) and six heavy metals (Pb, Ni, Cu, Cd, Zn and Cr) in the accumulated sludge in a 20-year old STRB in Denmark in order to assess the degradation and fate of these contaminants in a STRB and the relation to sludge composition. The results showed that the deposited sludge was dewatered to reach a dry matter content of 29%, and that up to a third of the organic content of the sludge was mineralized. The concentrations of heavy metals generally increased with depth in the vertical sludge profile due to the dewatering and mineralization of organic matter, but in all cases the concentrations were below the European Union legal limits for agricultural land disposal. The concentrations of fragrances and DEHP ranged from 10 to 9000 ng g−1 dry mass. The attenuation of hydrophobic micropollutants from the top to the bottom layer of the reed bed ranged from 40 to 98%, except for tonalide which increased significantly with sludge depth, and consequently showed an unusual depth distribution of the galaxolide/tonalide ratio. This unexpected pattern may reflect changes imposed by a long storage time and/or different composition of the fresh sludge in the past. The lack of a significant decreasing DEHP concentration with sludge age might indicate that this compound is very persistent in STRBs. In conclusion the STRB was a feasible technology for sludge treatment before its land disposal.