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- Kholoma, Ezekiel, 1972-, et al.
(författare)
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A review of the potential of reactive filter media in fortifying on-site wastewater treatment systems - Lessons from full-scale wastewater treatment systems Manuscript
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Wastewater with high concentrations of nutrients, pathogens and many micro-pollutants is usually satisfactorily treated by application of technologies which employ chemical processes. However, due to the absence of these processes in most small-scale wastewater treatment (SWT) systems, pollutants often escape treatment and ultimately end up in water bodies, hence the persistence of eutrophication and waterborne diseases experienced in many parts of world. Due to the recent introduction of requirements for SWT systems to comply with national discharge standards, alternative effective technologies are needed. Among the wide spectrum of supposedly effective alternative technologies which have been developed to-date, some can be incorporated to extend treatment chains of ineffective SWT facilities, e.g. package treatment plants and wetlands, while others are designed to enhance processes in some treatment steps, e.g. bioreactors for pre-treatment. However, due to the high costs, complexity and scarcity of many of these advanced technologies, reactive filter (RF) media are seemingly preferred. Much current knowledge about the potential of RF media is based on batch and column experimental findings. Therefore, various aspects of RF media relating to performance in full-scale plants are generally unknown. To our knowledge, no previous study has outlined the importance of key parameters distinguishing the performance of different RF media in full-scale plants or suggested the use of versatile media. This study therefore acquired and compiled data on RF media previously tested in full-scale plants, to compare and highlight parameters relating to their potential in treating wastewater of different strengths.
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| 2. |
- Kholoma, Ezekiel, 1972-, et al.
(författare)
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Filter media-packed bed reactor fortification with biochar to enhance wastewater treatment
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Contamination of water bodies with inappropriately released, poorly treated wastewater from rural establishments is a challenge world-wide. Rural communities in developed countries are now required to comply with statutory discharge limits, but less costly alternative technologies by which to comply are scarce. However, it is possible that retrofitting on-site facilities with specialist treatment units could provide a feasible solution. This study tested the effectiveness of retrofitting sand (Sa)- and gas-concrete (GC)-packed down-flow reactors with biochar (BC) in removing turbidity, dissolved organic carbon (DOC), phosphate (PO43-) and total phosphorus (TP) from wastewater. The reactors were each intermittently loaded with 0.063 L/d for 399 days. In general, all reactors achieved <3 NTU effluent turbidity (99% efficiency). The GC reactors were best at removing incoming PO43- (6.1 mg/L) and DOC (25.3 mg/L), trapping >95% and >60%, respectively. Compared with a reference Sa reactor (PO43- removal 35%; DOC removal 52%), the fortified sand (Sa-BC) filter removed significantly more PO43- (>45% removal, p=0.022) and DOC (>58% removal, p=0.034). In regression analysis, 53%, 81% and 85% of PO43- sorption variation in Sa, BC and Sa-BC filters, respectively, was explained by variations in reactor effluent pH. Similarly, a strong linear correlation was found between PO43- sorption efficiency and the pH of fortified (GC-BC, r > 0.7) and reference (r = 0.6) GC filters, suggesting chemisorption mechanisms. Therefore, if only sand is readily available for treating septic tank effluent, fortifying it with biochar could be a possible measure to improve its efficacy.
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| 3. |
- Kholoma, Ezekiel, 1972-
(författare)
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Fortification of soil-based wastewater treatment systems with versatile ubiquitous reactive media for enhanced removal of phosphorus and other pollutants
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Concerns about potential risks posed by discharge from small-scale wastewater treatment (SWT) systems to receiving water bodies have prompted robust enforcement of national discharge quality standards in rural areas of most developed countries. Consequently, communities in such places are in need of effective technologies with which to achieve compliance. Currently, reactive filter (RF) media are increasingly preferred over advanced alternatives, due mainly to their simplicity, affordability and proven potential. However, many of the field-tested filters are commercial products which are costly and scarce but also only capable of removing few contaminants they are engineered to target hence often requiring to be coupled with other treatment units to achieve full treatment. In the preliminary findings of this study, biochar (BC) was identified and thus suggested basing on existing literature, as a versatile ubiquitous low-cost material for treating wastewater. Its effectiveness in fortifying sand (Sa) and gas concrete (GC)-based SWT facilities was later demonstrated in long-term experiments using laboratory packed bed reactors and field constructed filter beds. The efficacy of SaBC and GCBC systems in reducing turbidity (>95%), DOC (60%; p<0.05) and PO43- (40-90%; p<0.05) was significantly higher than for their reference counterparts. Further, sorbed P was more leachable from Sa (11.2 mgkg-1) and SaBC (20.5 mgkg-1) filters but more extractable and hence plant-available in GC (65-91 mgkg-1). Therefore, the study concluded that fortification of soil-based systems with biochar filters may be a promising solution in enhancing performances of soil-based wastewater treatment systems, while P-rich RF media can act as a nutrient source for plants if recycled to agriculture.
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| 4. |
- Kholoma, Ezekiel, 1972-, et al.
(författare)
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Leachability and plant availability of phosphorus in post-sorption wastewater filters fortified with biochar
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Sand and gravel are widely applied in field filter systems for small-scale wastewater treatment. However, alternative filter materials are needed to achieve better treatment performance in removing contaminants and trapping plant nutrients for recycling to agriculture. This study assessed the plant availability and leachability of phosphorus (P) trapped in sand (Sa), biochar (BC) and gas concrete (GC, Sorbulite®) media used previously for phosphorus (P) removal in laboratory-scale packed bed reactors (PBR) and field-scale constructed filter beds (CFB). Phosphorus extraction and leaching were assessed in batch and leaching experiments using distilled water and ammonium lactate (AL) solution with a 1:20 solid:extractant ratio. The results revealed that both Sa (11.2 mgkg-1) and BC-fortified Sa (20.5 mgkg-1) leached P to percolating water, while P was less likely to leach from GC systems. Extraction with AL showed that the P retained in GC was plant-available and that the GC materials could release 65-90 mgkg-1 of the bound P mass. These findings highlight the need to evaluate the risk of nutrient leaching from filter media used in small-scale wastewater treatment systems with groundwater and surface water as final recipients. For greater sustainability, the P weakly bound in media such as sand and biochar and strongly bound in media such as gas concrete should be recovered by recycling the spent material to agriculture. However, this would require treatment system re-design to make recycling of filter material technically possible.
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