| 1. |
- Hamisi, Rajabu, 1978-, et al.
(författare)
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A new modelling approach for phosphorus mobility and retention processes in the Oxundaån catchment, Sweden
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Eutrophication is the most significant threat towater quality in the entire Baltic Sea region. Its causes are nutrientover-enrichment from diffuse and point sources. Thematic strategies forsustainable mitigation of phosphorus loss from sewage drainage systems andrunoffs from arable land require a holistic approach to identify the criticalpolluting sources and implement relevant policy for adaptive water qualitymanagement. The use of constructed wetlands constitutes one such strategy thatcan mitigate phosphorus loss. However, insufficient understanding about phosphorusmobility and retention in catchments significantly hinders efforts to identifysuitable sites for constructed wetlands and implement alternative, adaptive andeffective management actions. This study aims to evaluate the long-termphosphorus mobility and retention in the Oxudaån catchment in Sweden, andthereby propose suitable sites to localize constructed wetlands. The Soil andWater Assessment watershed model was applied to map and quantify the phosphorusloading from diffuse and point sources under the scenarios of land usemanagement practices. Simulation results have demonstrated the positivecorrelation between the phosphorus concentration with the surface runoffs andnegative correlation with the pH. Overall, Oxundaån catchment indicates a decreasingtrend of phosphorus loading in the Verkaån and Oxundaån riverine of around 2.1% and 1.3 % per year, respectively. The present study suggests the suitablesites for localizing constructed wetlands in the south-west and north-east ofOxundaån lake based on the factor of low slope topography and soilpermeability. The simulation results from the SWAT model offer evidence thatcan guide the localization and choice of management interventions to achieve asustainable mitigation of phosphorus loss. This study concludes that, while singlemanagement actions can help solve the problem of eutrophication, a moreeffective and sustainable mitigation of eutrophication will require the integrationof multiple adaptive land use management approaches.
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| 2. |
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| 3. |
- Hamisi, Rajabu, 1978-
(författare)
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Filtration System For On-Site Wastewater Treatment : Experiences From Modelling and Experimental Investigations
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many on-site wastewater treatment systems in Sweden are not sustainable in terms of treatment efficiency, nutrient recycling and economics. Achieving reliable and sustainable systems to meet on-site wastewater treatment demands requires comprehensive field investigations of the performance of novel technologies. This thesis investigated the performance of a new leading-edge technology for on-site wastewater treatment in a real field environment in northwest of Baltic Proper Sea, Sweden. The system integrates septic tank treatment technology with a package treatment plant (PTP) and a sequencing batch subsurface flow constructed wetland (SBCW). The investigation combined three approaches: field monitoring, laboratory-scale column experiments and process-based modelling, to provide a better understanding of system performance, predict contaminant retention and test system response to various environmental factors, design scenarios and operational conditions.The overall results indicated that the entire system is efficient in removing total phosphorus (83%), biological oxygen demand (BOD7, 99%) and Escherichia coli bacteria (89%). It is less efficient in total inorganic nitrogen removal (22%). Mean concentration of phosphorus (0.96 mg/L) and pH (8.8) in effluent from the entire system were found to be below the Swedish threshold values for on-site wastewater discharge. This indicates that the system could be reliable and sustainable technology for on-site wastewater treatment in cold climate conditions.A complementary three-dimensional (3D) model developed using COMSOL Multiphysics® software proved to be a useful and rapid tool for predicting the behaviour of complex hydraulic dynamics. It provided valuable insights into the spatial and temporal variability in sorption processes caused by changes in different wastewater treatment system design parameters, environmental factors and modes of operation. Through process-based modelling, a reactive filter material with longer lifetime and a SBCW design that improved the sustainability of on-site wastewater treatment system were successfully identified.It was concluded that long-term performance of reactive filter materials in PTP systems can be achieved when the system is loaded intermittently with low influent contaminant concentrations (<3 mg/L). Optimum phosphorus and nitrogen removal in SBCW can be achieved by manipulating drainage pipe placement and feeding mode, to enable longer contact time and artificial aeration conditions.
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| 4. |
- Hamisi, Rajabu, et al.
(författare)
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Long-term phosphorus sorption and leaching in sand filters for onsite treatment systems
- 2022
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 833, s. 155254-155254
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Tidskriftsartikel (refereegranskat)abstract
- The sorption capacities of sand filters used for onsite wastewater treatment and their associated risks of phosphorus (P) leaching on contact with rainwater were investigated in column experiments and with modelling tool for over 300 days. Columns packed with sand were exposed to real domestic wastewater of different characteristics and hydraulic loading modes. The wastewater fed into the columns was effluent collected from three different treatment units in the field: a septic tank (ST), biofiltration tank (BF) and Polonite® filter bag (PO). The risk of P leaching to groundwater and surface water was also assessed, by exposing the same sand columns to natural rainwater. Overall results indicated that sand soils can exhibit different adsorption and desorption capacities for electrical conductivity (EC), Total-P, phosphate-P and total suspended solids, depending on the characteristics of influent wastewater, loading rate and total operation time. The removal efficiencies of the sand columns increased in the order ST (98.16 %) > PO (93.36%) > BF (81.57%) for PO4-P and slightly decreased ST (97.11 %) > PO (92.06%) > BF (76.76%) for Total-P columns. All sand columns loaded with actual wastewater solutions from septic tanks and biofiltration tank have demonstrated high risks of phosphorus leaching (> 99.99%) to the groundwater. The modelling was successful captured behavior of EC tracer and adsorption of PO4-P with acceptable prediction uncertainty in the PO < 8% columns. The modelling results indicated that the decrease of loading rate from 83.3 mL d-1 to 20.83 mL d-1 led to an average increase of removal efficiency and prolong operational lifetime and mass of adsorbed Total-P in the sand soil. This study concludes that sand is a valuable filter medium at low loading rate for phosphorus removal in full-scale operations of onsite treatment systems, however very vulnerable for leaching P when in contact with rainwater.
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| 5. |
- Hamisi, Rajabu, 1978-
(författare)
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Modelling phosphorus dynamics in constructed wetlands upgraded with reactive filter media
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Developing low-cost and effective technologies to upgrade phosphorus (P) removal from the catchment runoffs and rural wastewater treatment facilities is one of the main research agendas to save the Baltic Sea from eutrophication. In Sweden, the construction of the constructed wetlands has been one of the environmental objectives for wastewater quality improvement in the small communities. However, the insufficiently understanding of the mechanisms underlying the process of phosphorus mobility and sorption in the constructed wetlands has limited design of the effective constructed wetlands. To provide the better understanding of sorption process in the catchment and constructed wetland system, this thesis used the GIS-based Soil and Water Assessment Tool (SWAT) to predict phosphorus mobility and identify the critical diffusing sources of phosphorus loss in the Oxunda catchment (Paper I). Then, the study developed the three-dimensional numerical Reactive TRAnsPort Model (RETRAP - 3D) in the COMSOL Multiphysics® for evaluating the long - term sorption processes and removal efficiencies of the porous reactive media for upgrading the performance of constructed wetlands (Paper II and III). The latter model coupled many physics equations to solve process of water flow, reaction kinetics and solute transport in the porous reactive adsorbent media for application in the constructed wetlands. The data from the field measurements and column experiments have been used to demonstrate the model simulation accuracy to capture the process of phosphorus sorption in the real environment. Modeling results ranked the phosphorus removal efficiency of the adsorbent media as follows: Polonite® (88 %), Filtralite P® (85%), BFS (62%), Wollastonite (57 %). The satisfactory agreement which obtained between the simulated outputs and measured data confirmed that the SWAT and RETRAP-3D are useful tools for describing various processes in the complicated system. However, further study is required to generate and validate more experimental data to evaluate the sensitivity of local parameters.
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| 6. |
- Hamisi, Rajabu, 1978-, et al.
(författare)
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Modelling phosphorus recovery by reactive adsorbent in a vertical subsurface flow constructed wetland
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Phosphorus removal efficiencies by four low - costsreactive adsorbent media were evaluated in the long - time period using thethree - dimensional model of the vertical subsurface flow constructed wetlandsin the COMSOL Multiphysics® software. Evaluations were made for Polonite,Filtralite P, Sorbulite and Wollastonite adsorbent media with the aims ofpredicting their long - term sorption capacity and describing the phenomena ofsorption mechanisms when applied in the vertical subsurface flow constructedwetlands for wastewater purification. The 3D model of the vertical flowconstructed wetlands were dimensioned to Swedish EPA guidelines for small scalewastewater treatment, and calibrated at saturated media using the breakthroughdata derived from the column experiments of similar adsorbent mediaapplication, and the local sensitivity analysis were performed for waterquality and hydraulic loading parameters. It was observed that the breakthroughcurves developed by model were significantly correlated to the experimentaldata. The overall findings showed that Polonite® could be the potentialreactive adsorbent for phosphorus removal in the VF-CWs application, and itsremoval efficiency was discovered to last for 5 years. The large variation ofmedia sorption capacities discovered to be affected more by factor of pH andhydraulic loading rates than the particle size. High degree of predictionaccuracy which is demonstrated by this model suggest that the proposed model isa useful tool for predicting pollutants removal in various reactive porousmedia.
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| 7. |
- Hamisi, Rajabu, et al.
(författare)
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Modelling phosphorus sorption kinetics and the longevity of reactive filter materials used for on-sitewastewater treatment
- 2019
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Ingår i: Water. - : MDPI AG. - 2073-4441. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- Use of reactive filter media (RFM) is an emerging technology in small-scale wastewater treatment to improve phosphorus (P) removal and filter material longevity for making this technology sustainable. In this study, long-term sorption kinetics and the spatial dynamics of sorbed P distribution were simulated in replaceable P-filter bags filled with 700 L of reactive material and used in real on-site treatment systems. The input data for model calibration were obtained in laboratory trials with Filtralite P®, Polonite® and Top16. The P concentration breakthrough threshold value was set at an effluent/influent (C/C 0 ) ratio of 1 and simulations were performed with P concentrations varying from 1 to 25 mg L -1 . The simulation results showed that influent P concentration was important for the breakthrough and longevity, and that Polonite performed best, followed by Top16 and Filtralite P. A 100-day break in simulated intermittent flow allowed the materials to recover, which for Polonite involved slight retardation of P saturation. The simulated spatial distribution of P accumulated in the filter bags showed large differences between the filter materials. The modelling insights from this study can be applied in design and operation of on-site treatment systems using reactive filter materials.
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| 8. |
- Hamisi, Rajabu, et al.
(författare)
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Optimization of on-site wastewater treatment efficiency and recovery based on nutrient mobility and adsorption kinetics modelling using HYDRUS-2D coupled with PHREEQC
- 2024
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 492
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Tidskriftsartikel (refereegranskat)abstract
- A closed-loop on-site wastewater treatment system (OWT) was studied comprising steps of septic tank to remove organics (Biological Oxygen Demand (BOD)), biofiltration clarifier for biological removal of nitrogen (N), phosphorus (P) and BOD, reactive Polonite® filter for chemical adsorption and precipitation removal of dissolved P, and tidal flow constructed wetland (TFCW) sand filter for polishing the effluent to low P and N effluent Swedish standards. The field experimental data that have been used to optimize TFCW design in the numerical modelling using HYDRUS-2D coupled with and without PHREEQC indicated that the adsorption efficiency of the reactive Polonite® adsorbent was nearly double to that obtained in TFCW sand filters for PO4-P (95 %) and Total-P (85 %) removal in summer at a high temperature range (15.4–18.8 °C) and pH range (9.9–10.8). The weaker PO4-P (53 %) and Total-P (25 %) removal efficiency in winter was due to a low temperature (1.5–8.1 °C) and low pH (7.2–7.9). This decrease in pH was attributed to salinity in the domestic wastewater and dilution of rainwater. Modelling results revealed that the transport mechanisms and rate of P adsorption kinetics in the TFCW sand filters enhanced with calcium and iron flow from chemical dissolution in the preceding Polonite® adsorbent was increased with the increase in temperature. However, the P adsorption was less sensitive at high ferrihydrite (Fe(OH)3) dose, suggesting limited effects of cations dissolution and abundance of metal oxides and hydroxide ions at the mineral surface for anions exchange with phosphate for surface complexation. The strategy of combining field data and modelling provided valuable insights for assessing adaptability and optimizing TFCW design under variable fluxes and scenario effects of insulated/uninsulated and dilution by rainwater in cold-climate regions.
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| 9. |
- Hamisi, Rajabu, et al.
(författare)
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Performance of a tidal flow constructed wetland used for post-treatment of on-site wastewater in cold climate
- 2022
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Ingår i: Journal of Water Process Engineering. - : Elsevier BV. - 2214-7144. ; 47
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Tidskriftsartikel (refereegranskat)abstract
- The performance of a tidal flow constructed wetland (TFCW) following wastewater treatment in a package plant designed for two households was studied in a nine-month field trial and its design evaluated through process modelling and pumping tests. The TFCW is operated by filling and draining periods lasting five to nine days, depending on wastewater production by users. The effects of passive aeration, temperature, influent concentration of nutrients and bacteria as well as hydraulic loading on the treatment efficacy of the TFCW system were studied. Results showed that the TFCW system removed ammonium-nitrogen (NH4-N, 76%), phosphate -phosphorus (PO4-P, 56%), total inorganic nitrogen (TIN, 28%) and reduced water pH by15%. The removal efficiency of TIN was significantly improved in the summer (> 50%). The average influent concentration of total phosphorus (TP) was low after the preceding package plant treatment (1.12 mg L-1), but the TFCW showed ability to further reduce TP to the average concentration of 0.57 mg L-1. A coupled reactive transport model was developed in the COMSOL Multiphysics (R) 5.6 software to predict processes of water flow and was validated against the actual data from the field. The modelling exhibited a satisfactory prediction accuracy and capability to capture behavior of effluent PO4-P, NH4-N and dissolved oxygen concentration. Moreover, modelling processes helped to understand the defects of water flow and adsorption processes within the treatment wetland.
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| 10. |
- Hamisi, Rajabu, et al.
(författare)
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Performance of an On-Site Wastewater Treatment System Using Reactive Filter Media and a Sequencing Batch Constructed Wetland
- 2019
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Ingår i: Sustainability. - : MDPI. - 2071-1050. ; 11:11
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Tidskriftsartikel (refereegranskat)abstract
- Many on-site wastewater treatment systems, such as soil treatment systems, are not sustainable in terms of purification efficiency, nutrient recycling potential, and economics. In this case study, a sequencing batch constructed wetland (SBCW) was designed and added after a package treatment plant (PTP) using reactive filter media for phosphorus (P) removal and recycling. The treatment performance of the entire system in the start-up phase and its possible applicability in rural areas were investigated. Raw and treated effluents were sampled during a period of 25 weeks and analyzed for nitrogen, phosphorus, BOD7, and bacteria. Field measurements were made of wastewater flow, electrical conductivity, oxygen, and temperature. The entire system removed total-P and total inorganic nitrogen (TIN) by 83% and 22%, respectively. High salt concentration and very low wastewater temperature were possible reasons for these unexpectedly low P and TIN removal efficiencies. In contrast, removal rates of bacteria (Escherichia coli, enterococci) and organic matter (as BOD) were high, due to filtration in the alkaline medium Polonite((R)) (Ecofiltration Nordic AB, Stockholm, Sweden) and the fine sand used as SBCW substrate. High pH in effluent from the PTP was efficiently reduced to below pH 9 in the SBCW, meeting recommendations by environmental authorities in Sweden. We concluded that treating cold on-site wastewater can impair treatment performance and that technical measures are needed to improve SBCW performance.
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