Browsing by Subject "wastewater treatment"

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  • Simha, Prithvi; Karlsson, Caroline; Viskari, Eeva-Liisa; Malila, Riikka; Vinnerås, Björn (Frontiers Media S.A., 2020)
    Frontiers in Environmental Science 8, 11.9.2020
    Alkaline dehydration can treat human urine to produce a dry and nutrient-rich fertilizer. To evaluate the technology at pilot-scale, we built a prototype with capacity to treat 30 L urine d−1 and field tested it for the first time at a military training camp in Finland. We operated the system for 3 months and monitored the recovery of nutrients, end-product composition, physicochemical properties and energy consumption. Results revealed that the system received less urine than anticipated, but achieved high dehydration rates (30–40 L d−1m−2), recovered 30 ± 6% N, and yielded end-products with 1.4% N, 0.9% P, and 8.3% K. However, we demonstrated that the system had potential to recover nearly 70% N and produce fertilizers containing 13.2% N, 2.3% P, and 6.0% K, if it was operated at the design capacity. The energy demand for dehydrating urine was not optimized, but we suggested several ways of reducing it. We also discussed concerns surrounding non-essential heavy metals, salts, and micropollutants, and how they can be overcome to safely recycle urine. Lastly, we pointed out the research gaps that need to be addressed before the technology can be implemented at larger scale.
  • Hultman, Jenni; Tamminen, Manu; Pärnänen, Katariina; Cairns, Johannes; Karkman, Antti; Virta, Marko (2018)
    Wastewater treatment plants (WWTPs) collect wastewater from various sources for a multi-step treatment process. By mixing a large variety of bacteria and promoting their proximity, WWTPs constitute potential hotspots for the emergence of antibiotic resistant bacteria. Concerns have been expressed regarding the potential of WWTPs to spread antibiotic resistance genes (ARGs) from environmental reservoirs to human pathogens. We utilized epicPCR (Emulsion, Paired Isolation and Concatenation PCR) to detect the bacterial hosts of ARGs in two WWTPs. We identified the host distribution of four resistance-associated genes (tetM, int1, qacE Delta 1 and bla(OXA-58)) in influent and effluent. The bacterial hosts of these resistance genes varied between the WWTP influent and effluent, with a generally decreasing host range in the effluent. Through 16S rRNA gene sequencing, it was determined that the resistance gene carrying bacteria include both abundant and rare taxa. Our results suggest that the studied WWTPs mostly succeed in decreasing the host range of the resistance genes during the treatment process. Still, there were instances where effluent contained resistance genes in bacterial groups not carrying these genes in the influent. By permitting exhaustive profiling of resistance-associated gene hosts in WWTP bacterial communities, the application of epicPCR provides a new level of precision to our resistance gene risk estimates.
  • Salmi, Pauliina; Ryymin, Kalle; Karjalainen, Anna K.; Mikola, Anna; Uurasjärvi, Emilia; Talvitie, Julia (IWA Publishing, 2021)
    Water Science & Technology
    Microplastics (MPs) from households, stormwater, and various industries are transported to wastewater treatment plants (WWTPs), where a high proportion of them are captured before discharging their residuals to watersheds. Although recent studies have indicated that the removed MPs are mainly retained in wastewater sludge, sludge treatment processes have gained less attention in MP research than water streams at primary, secondary, and tertiary treatments. In this study, we sampled 12 different process steps in a tertiary-level municipal WWTP in central Finland. Our results showed that, compared to the plant influent load, three times more MPs circulated via reject water from the sludge centrifugation back to the beginning of the treatment process. Fibrous MPs were especially abundant in the dewatered sludge, whereas fragment-like MPs were observed in an aqueous stream. We concluded that, compared to the tertiary effluent, sludge treatment is the major exit route for MPs into the environment, but sludge treatment is also a return loop to the beginning of the process. Our sampling campaign also demonstrated that WWTPs with varying hydraulic conditions (such as the one studied here) benefit from disc filter-based tertiary treatments in MP removal.
  • Vuori, Larissa (Helsingin yliopisto, 2019)
    Microplastic pollution is a globally increasing issue in both terrestrial and aquatic environments. One of its pathways to ecosystems is urban wastewater, as the treated effluent has been observed to contain remarkable quantities of plastic particles. In addition, as the treatment process separates the nutrients and solids into a sludge, the particles have been found in the sludge as well. The aim of this thesis is to investigate the costs of removing microplastic particles from the wastewater, and to assess the total microplastic pollution mitigation potential of selected wastewater treatment and sludge management methods. To examine this, I conducted a cost-effectiveness analysis, in which I constituted five different technology scenarios and calculated their incremental cost-effectiveness ratios. The ratios were then compared against a business-as-usual baseline scenario and each other to define the lowest cost of removing microlitter. The cost-effectiveness analysis was conducted for four different wastewater treatment plant sizes. The technology scenarios constituted of combinations of three wastewater treatment and two sludge management methods. The wastewater treatment methods were conventional activated sludge, rapid sand filtering and membrane bioreactor, and the sludge management methods were anaerobic treatment followed by land application as a fertilizer, and sludge incineration. The cost data on the selected wastewater treatment and sludge management methods were obtained from various documented sources, whereas two studies on the microlitter content in wastewater (Talvitie et al., 2017a & 2017b) comprised the effect data. To achieve an overview of the magnitude and the mitigation capacity of the issue, I compared the costs and the quantity of released microlitter of each technology scenario to the baseline scenario. In addition, to assess the impact of changing economic attributes and wastewater quality on the cost-effectiveness ratios, I performed a univariate sensitivity analysis. The results of the analyses prove that removing microplastics from wastewater is both feasible and cost-effective. The membrane bioreactor combined with sludge incineration resulted the most economical scenario in all circumstances and in each wastewater treatment capacity.
  • Esfahani, Reza (Helsingfors universitet, 2016)
    Wastewater produced by the mining industry can be very acidic and high in dissolved metals. If released to the environment, it initiates diverse issues some of which are increasing acidity and high heavy metal concentrations. Wastewater treatment is traditionally done by using manufactured chemicals which is neither environmentally nor economically sound. The use of industrial by-product geomaterials is a low-cost alternative wastewater treatment method as these materials are anyway produced in other industries. In wastewater treatment with geomaterials, the element removal mechanism is based on precipitation and surface adsorption which are highly pH dependent. In this study, acidic multimetal wastewater from Talvivaara was treated with three byproducts (steel slag, apatite mine tailings and Sachtofer PR) of Finnish industries. Waste water was incubated with geomaterials for 1, 7 and 21 days, then titrated to pH 7. Effect of geomaterials and time on waste water pH and base consumption required to increasing the pH, as well as on concentrations of iron, aluminum, nickel, zinc, manganese, sodium and sulfur were studied. Untreated wastewater pH decreased with time due to hydrolyses of metals. Oxidation of ferrous iron to ferric iron also seemed to contribute to acidification of wastewater. Thus the base consumption increased significantly with incubation time. Among the used solids, steel slag most efficiently increased pH and consequently decreased the consumed base. Steel slag also showed the best results in element removal. It removed all or significant amount of dissolved iron, aluminum, nickel, manganese and sulfur. Tailings and Sachtofer PR showed poor results regarding element concentration by releasing several elements to the solution.