Steel Slag Filter Research Articles

Steel Slag and Limestone as a Rock Filter for Eliminating Phosphorus from Domestic Wastewater: A Pilot Study in a Warm Climate

Phosphorus input with excessive use of fertilizers and manure as one of the main sources of nutrient pollution has increased recently in the wastewater as result of intensive farming and industrialized and densely populated areas. The novelty of the current work lies in improving a Vertical Aerated Rock Filter (VARF) using steel slag and limestone media to enhance the efficiency of a rock filter (RF) to eliminate total phosphorus (TP) from domestic wastewater. RF was designed with steel slag and limestone (calcium hydroxide) as a pilot scale called vertical aerated steel slag filter (VASSF) and optimized based on hydraulic loading rates (HLR) (0.16 to 5.44 m3/m3 day) and airflow rates ranging from 3 to 10 L/min. The highest removal for the design of the laboratory scale steel slag filter (LSSSF) was achieved by approximately 58%, while for the laboratory-scale limestone filter (LSLSF), it was 64%. The VASSF achieved a removal percentage at 30% of TP, biological oxygen demand (BOD; 89%), chemical oxygen demand (COD; 75%), total suspended solids (TSS; 73%), and total coliforms (TC; 96%), recorded with 7 L/min of an airflow rate and 1.04 m3/m3.day of hydraulic loading rate (HLR) at potential of hydrogen (pH) 7.3 and 5.09 mg/L of dissolved oxygen (DO). These findings indicated that the steel slag is higher than limestone in TP removal, because of ion exchange between phosphorus hydrolysis and the adsorption process. Moreover, in the pilot study, the removal efficiency needs more investigation to determine the best conditions for TP considering the temperature, which is unstable, and presence of other pollutants, which might negatively affect the removal efficiency under unstable conditions.

Determination of Phosphorus Removal Mechanism in Aerated and Unaerated Steel Slag Filter System as Secondary Treatment System for Textile Industrial Wastewater

Phosphorus is the element that promotes growth in plant. However, over loading of phosphorus into surfaces water leads to severe environmental problems known as eutrophication. Improper treatments of phosphorus removal prior discharges from industrial effluent are one of the contributions to eutrophication. Textile effluent is one of the sources of phosphorus loading in surface water with concentration of 1-9 mg/L P. Since attentions are given in removing the color from the effluent, phosphorus is commonly ignored in wastewater treatment system. Thus, the study of phosphorus removal in textile wastewater is conducted using steel slag system filter under aerated (ASSF) and unaerated (USSF) condition. The systemwas set up for influent pHrange of 5.30-7.00 at primary treated wastewaterfor textile wastewaterunder aerated and unaerated condition. Sampling was done twice a week for 12 weeksand analyzed for Total phosphorus concentration. The Activated Carbon(ACF)filterin the existing treatment system is also sampled to compare the removal efficiency The USSFfilter shows better removal than ASSFfilter with46% to 70%of efficiency removal.Meanwhile, the removal efficiency of ASSF is 37% to 66%.The adsorbate formed in ASSF is analyzed using SEM-EDX and the precipitation formed in USSF is analyzed using XRD.This shows that steel slag filter provides promising result in phosphorus removal.

Removal of Phosphorus from Domestic Wastewater by Using L-shape Semi Aerated Steel Slag Filter System

Excessive amount of phosphorus in wastewater prior discharged are one of the major cause of eutrophication in lakes and rivers making phosphorus removals are essentials. However, removing phosphorus from wastewaters required a high cost treatment system to be installed at treatment facilities. To provide alternative solutions, this study was conducted to investigate the effectiveness of L-shape semi aerated filter with steel slag as filter media to provide a cost effective treatment system using natural media as a solution to remove phosphorus from domestic wastewater. The L-shaped semi aerated filter was constructed and installed onsite at Sewage Treatment Plant (STP) UTHM. Then, the laboratory test was conducted twice a week to analyse five parameters including pH, turbidity, dissolved oxygen (DO), chemical oxygen demand (COD), and total phosphorus (TP). The results showed that the effluent from the L-shape steel slag filter was alkaline with a pH value range of 7.22 to 9.71 due to alkaline properties of steel slag. Turbidity value of effluent at vertical section was higher than horizontal section as it may affect the COD removal of the filter. In the vertical system, the DO value range was higher (1.5 to 6.9 mg/L) than the horizontal system (1.27 to 5.5 mg/L) since oxygen was introduced by aeration process. Furthermore, this system showed good COD removal efficiencies with values ranged from 10% to 76%. Lastly, total phosphorus removal efficiencies also showed great removals with range of 29% to 68%. From the results obtained, steel slag with high-Ca content showed excellent potential in removing phosphorus from domestic wastewater.

Study of Steel Slag Filter Unit as a Secondary Treatment System for Removing Total Phosphorus from Textile Industry Wastewater

Eutrophication is one of the global concerned due to algae bloom in the natural surface water such as lakes and swamp area. Industrial effluent with incomplete treatment discharged has become one of the main culprits to this phenomenon. Approximately, 0.3 – 13 mg/L of total phosphorus can be found in the final discharge of industrial effluent showing that the existing treatment including an activated carbon filter (ACF) has limitation in polishing the phosphorus. Therefore, this 16 week of study has been designed to study the alternative treatment phosphorus removal at secondary stage to replace the tertiary treatment by using steel manufacturing by-product as filter media for effective phosphorus removal from the textile industry wastewater. Two units of lab-scale vertical steel slag filter (SSF) systems under aerated and unaerated conditions have been developed for this study. The samples were collected and analysed biweekly for selected parameters including pH, alkalinity, DO and TP. The results obtained from this study show that the unaerated steel slag filter has a high efficiency of TP removal which ranged from 46% to 70% compared to the aerated SSF with removal efficiency ranged from 37% to 66%. Besides, the existing ACF removal efficiency was ranged from 36% to 54%. Thus, the use of steel slag in removing phosphorus from textile wastewater is possible with the used of both aerated and unaerated steel slag filter systems. Furthermore, the removal mechanism involved was likely to be precipitation and adsorption.

Optimizing vertical flow aerated steel slag filter system with nitrifiers bacteria for nutrients' removal from domestic wastewater: a pilot study

AbstractBACKGROUNDThe present study aimed to optimize the removal efficiency of ammonia nitrogen (NH3‐N) and total kjeldhal nitrogen (TKN) from domestic wastewater as a function of hydraulic loading rates (HLRs) (0.16–5.44 m3 m–3 day–1) and the aeration rate (3, 5 and 10 L min–1) in a vertical flow aerated steel slag filter (VFASSF) system with nitrifier bacteria. The nitrifier bacterial cell morphology was determined using scanning electron microscopy (SEM) analysis.RESULTSThe HLRs affected the performance of the VFASSF in removing TKN and NH3‐N from domestic wastewater. The optimal air flow rate for removing NH3‐N and TKN was recorded with 10 L min–1 and HLR 2.72 m3 m–3 day–1, at which the removal efficiency was >91% compared to 90% and 88% with 3 L min–1 and 5 L min–1 air flow rate, respectively. The high removal was a consequence of the high aeration which enhances the nitrification process performed by the nitrifying bacteria in the VFASSF.CONCLUSIONSThese findings reflected the applicability of VFASSF in the treatment and removal of nutrients from domestic wastewater. © 2020 Society of Chemical Industry

Chemical Clogging and Evolution of Head Losses in Steel Slag Filters Used for Phosphorus Removal

The objective of this study was to propose a conceptual model of clogging in alkaline granular filters. Two slag columns were operated for 600 days and monitored using piezometers and tracer tested at regular intervals. The type of influent (organic or inorganic) affected the loss of effective porosity in the filters. Well organized and loose crystal structures were observed by scanning electron microscopy in columns with inorganic and organic influents, respectively. It was postulated that the formation of crystals in unorganized structures results in confined voids that are not accessible for water flow, thus accelerating porosity loss. The effect of the combination of chemical clogging and biofilm on the porosity loss is higher than the effect of these two factors separately. The Kozeny-Carman equation for hydraulic conductivity could not efficiently predict the evolution of head losses in the column fed with an inorganic influent. The crystal structure and connectivity in the presence of homogeneous or heterogeneous precipitation are concepts that could improve predictions of hydraulic conductivity. The results of this study highlighted the importance of the inlet zone on the development of pressure head in alkaline granular filters. Future research on clogging should focus on precipitation mechanisms in the inlet zone and on the design of the feeding system.

Phosphorus Removal and Carbon Dioxide Capture in a Pilot Conventional Septic System Upgraded with a Sidestream Steel Slag Filter

The objective of this work was to demonstrate the removal of the phosphorus and carbon dioxide capture potential of a conventional septic system upgraded with a sidestream steel slag filter used in recirculation mode. A pilot scale sidestream experiment was conducted with two septic tank and drainfield systems, one with and one without a sidestream slag filter. The experimental system was fed with real domestic wastewater. Recirculation ratios of 25%, 50% and 75% were tested. Limestone soils and non-calcareous soils were used as drainfield media. The tested system achieved a satisfactory compromise between phosphorus removal and pH at the effluent of the septic tank, thus eliminating the need for a neutralization step. The phosphorus removal efficiency observed in the second compartment of the septic tank was 30% in the slag filter upgraded system, compared to −3% in the control system. The slag filter reached a phosphorus retention of 105 mg/kg. The drainfield of non-calcareous soils achieved very high phosphorus removal in both control and upgraded systems. In the drainfield of limestone soil, the slag filtration reduced the groundwater phosphorus contamination load by up to 75%. The removal of chemical oxygen demand of the drainfields was not affected by the pH rise induced by the slag filter. Phosphorus removal in the septic tank with a slag filter was attributed to either sorption on newly precipitated calcium carbonate, or the precipitation of phosphate minerals, or both. Recirculation ratio design criteria were proposed based on simulations. Simulations showed that the steel slag filter partly inhibited the biological production of carbon dioxide in the septic tank. The influent alkalinity strongly influenced the recirculation ratio needed to raise the pH in the septic tank. The recirculation mode allowed clogging mitigation compared to a mainstream configuration, because an important part of chemical precipitation occurred in the septic tank. The control septic tank produced carbon dioxide, whereas the slag filter-upgraded septic tank was a carbon dioxide sink.

Aerated and unaerated steel slag filter systems as polishing unit for phosphorus removal from textile industrial effluent

Improper tertiary treatment of industrial effluent discharged causes an excessive phosphorus input which leads to eutrophication. Excessive growth of algae will degrade the natural ecosystem of surface waters. Conventional treatment such as activated carbon filter used as a polishing unit in the tertiary treatment is unable to eliminate the phosphorus completely. Approximately, 0.3–15 mg/l of phosphorus still presents in the final discharge of industrial effluent. Therefore, this study is conducted to provide alternative solutions using natural treatment with cost saving materials to further remove phosphorus from the textile industrial effluent. Aerated and unaerated lab-scale steel slag filters systems were run for 12 weeks at water treatment plant. The sample collected was analyzed twice a week for the parameters of pH, alkalinity, temperature, dissolved oxygen, total phosphorus, chemical oxygen demand, and total suspended solid. The results of this study showed that the unaerated steel slag filter (USSF) has a high percentage of phosphorus removal compared to aerated steel slag filter (ASSF) which is 55% to 86% while ASSF have removal efficiency of 52% to 71%. However, the removal efficiency of activated carbon filter (ACF) used in treatment plant is slightly better than ASSF which is 52% to 81%. The mechanism of removal involved is likely to be through adsorption.

Phosphorus Removal from Textile Industrial Wastewater using Aerated High Calcium Steel Slag Filter System

Phosphorus in wastewater accelerates eutrophication in water body. Textile wastewater is one of contributors to the phosphorus loading into water body which promotes the growth of algae, reducing the oxygen content and detrimental to surface water ecosystem. Myriad existing treatments for phosphorus removal have been developed but it requires a high cost treatment and maintenance. Rock filter system emerged as one of the alternative method for phosphorus removal from wastewater with steel slag as the filter media. However, application of the system in treating industrial wastewater is still unclear especially in big scale application and requires extensive study. This study is done to provide solution of phosphorus loading from textile wastewater using steel slag as filter material and to investigate the removal capacity of steel slag with high calcium and low ferum content. The steel slag was analyzed using XRF for its composition and to ensure the steel slag has high Ca content. Then, the aerated steel slag filter system was set-up on the site of textile industry for a month and analyzed according to parameter of pH, alkalinity, COD, DO, temperature and TSS. The result from this study showed that the aerated high calcium low ferum steel slag filter has a high efficiency of phosphorus removal rates varied from 35% to 67% in treating textile wastewater. It was found that aerated steel slag system was efficient in phosphorus removal by using industrial wastewater.

Performance of carbon nanotube-coated steel slag filter media for the removal of phosphorus and heavy metal in stormwater

Performance of carbon nanotube-coated steel slag filter media for the removal of phosphorus and heavy metal in stormwater

Investigation of PO43- Removal in Aerated and Unaerated High Fe EAF-Slag Filter System

Phosphorus in wastewater is one the main culprit which accelerates eutrophication in waterbody if it is not being treated properly. Steel slag filter emerged as one alternative treatment for wastewater. However, the variousness of metal oxides including Fe in steel slag will affect the phosphorus removal efficiency. Thus, this study was conducted to investigate the ability of a series of lab-scale high Fe electric arc furnace (EAF- slag) column filters in removing PO43- from synthetic wastewater. The systems were operated under aerated and unaerated within acidic and alkaline conditions. Synthetic wastewater contained 25 mg/L was prepared as the feed and monitored weekly basis for the PO43- removal efficiency and the total metals (Ca, Fe, and Mg) concentrations in the effluents. The results show that both aerated and unaerated high Fe EAF-slag filter systems have high PO43- removal efficiency under acidic condition, which unaerated system performed slightly better. It can be observed that unaerated systems performed better in removing PO43- at acidic and neutral pH values but not at extremely high pH. As for the PO43- removal mechanism was achieved by adsorption and precipitation at acidic pH and the concentration of Ca, Mg and Fe in effluents was related to the PO43- removal efficiency at different pH values.

Steel slag filter design criteria for phosphorus removal from wastewater in decentralized applications

The objective of this project was to develop a novel phosphorus removal system using steel slag filters applicable in decentralized applications and to propose design criteria about maintenance needs. Slag exhaustion functions were measured on 2–3 mm, 3–5 mm, 5–10 mm and 16–23 mm slag. Three steel slag columns with particle size of 2–3 mm, 3–5 mm and 5–10 mm were fed with the effluent of an aerated lagoon during 589 days. A barrel reactor test was fed during 365 days with the effluent of an attached growth aerated biological reactor. The o-PO4 concentration at the effluent of the 2–3 mm and 3–5 mm columns and barrel reactor test was between 0.04 and 0.3 mg P/L. Particulate phosphorus, however, was removed by about 50%. The P-Hydroslag model implemented in PHREEQC was successfully calibrated with data from the column test, and validated with data from the barrel reactor test. The calibrated model was used to simulate long-term operation of a slag barrel reactor with two parallel streams of five replaceable steel slag barrels, with total hydraulic retention time of voids of 15 h. The system longevity was strongly influenced by the influent alkalinity. The simulated longevity was 7 years with an influent alkalinity of 50 mg CaCO3/L and 2 years with an influent of 210 mg CaCO3/L. The alkalinity of the steel slag filter influent was influenced by the type of aquifer supplying drinking water, the presence of nitrification activity and by the CO2 concentration in the enriched air of the upstream biological process. Simulated scenarios with partial barrel replacement (e. g. barrels 1 and 2 out of 5 replaced at frequency of 0.5, 1, 1.5, 2, 2.5, 3, 3.5 or 4 years) increased the system longevity up to 14 years while slightly increasing the number of barrels needed.

The Effects of PO43- Removal from Aqueous Solution with Varied Concentrations of Metal Oxides in Steel Slag Filter System

High amount of orthophosphate will accelerate the growth of autotrophs and eutrophication will occur. This phenomenon decreases the water quality and as a result may increase the cost of water treatment for drinking water. The overabundance of orthophosphate occurs when untreated or inadequately-treated wastewater from domestic and industrial activities is released into water bodies. Conventional treatment has been developed to treat wastewater. However, it is not effective for phosphorus removal, hence, high-cost advanced treatment is needed to remove phosphorus. Thus, alternative low-cost treatments for phosphorus removal are needed. Therefore, this study was conducted to understand and investigate the mechanisms of phosphorus removal using two different setups of steel slag filter, Set 1 for high Fe and Set 2 for high Ca. The study was operated at different pH values of 3, 5, 7, 9 and 11 under aerated and unaerated conditions. The samples of steel slag from 12 filters that has been run for three months for each set were semi-quantitatively analysed using scanning electron microscope-energy dispersive X-ray (SEM-EDX) to identify the adsorption of phosphate ion on the surface of the steel slag. The results of SEM-EDX studies showed that adsorption mechanism of phosphate removal takes place on the surface of the steel slag. The precipitates in the steel slag filters were collected and analysed for X-ray diffraction (XRD) for chemical compound identification and the precipitates were confirmed to be Fe3O4, a precursor of iron phosphate related compound.

Study on Key Factors of Adsorption of Phosphorus by Steel Slag Filter Based on Response Surface Method

Excessive phosphorus emission is one of the important reasons for the eutrophication of water. At the same time, phosphorus is a significant mineral resource. In this paper, the response surface method is used to study the key influencing factors of phosphorus removal by steel slag filter and its action. Four factors affecting the dosage, initial pH, reaction time and calcium-phosphorus molar ratio were selected. The phosphorus removal was used as the response value. The interaction between various factors was established by Box-Behnken response surface analysis. The optimal conditions were determined by equation regression analysis: dosage = 2 cm3; initial pH = 7; molar ratio of calcium to phosphorus was 2:1; reaction time = 2 h.

Development and modelling of a steel slag filter effluent neutralization process with CO2-enriched air from an upstream bioprocess

The main objective of this project was to develop a steel slag filter effluent neutralization process by acidification with CO2-enriched air coming from a bioprocess. Sub-objectives were to evaluate the neutralization capacity of different configurations of neutralization units in lab-scale conditions and to propose a design model of steel slag effluent neutralization. Two lab-scale column neutralization units fed with two different types of influent were operated at hydraulic retention time of 10 h. Tested variables were mode of flow (saturated or percolating), type of media (none, gravel, Bionest and AnoxKaldnes K3), type of air (ambient or CO2-enriched) and airflow rate. One neutralization field test (saturated and no media, 2000–5000 ppm CO2, sequential feeding, hydraulic retention time of 7.8 h) was conducted for 7 days. Lab-scale and field-scale tests resulted in effluent pH of 7.5–9.5 when the aeration rate was sufficiently high. A model was implemented in the PHREEQC software and was based on the carbonate system, CO2 transfer and calcite precipitation; and was calibrated on ambient air lab tests. The model was validated with CO2-enriched air lab and field tests, providing satisfactory validation results over a wide range of CO2 concentrations. The flow mode had a major impact on CO2 transfer and hydraulic efficiency, while the type of media had little influence. The flow mode also had a major impact on the calcite surface concentration in the reactor: it was constant in saturated mode and was increasing in percolating mode. Predictions could be made for different steel slag effluent pH and different operation conditions (hydraulic retention time, CO2 concentration, media and mode of flow). The pH of the steel slag filter effluent and the CO2 concentration of the enriched air were factors that influenced most the effluent pH of the neutralization process. An increased concentration in CO2 in the enriched air reduced calcite precipitation and clogging risks. Stoichiometric calculations showed that a typical domestic septic tank effluent with 300 mg/L of biodegradable COD provides enough biological CO2 for neutralization of a steel slag effluent with pH of 10.5–11.5. A saturated neutralization reactor with no media operated at hydraulic retention time of 10 h and a concentration of 2000 ppm in CO2 enriched air is recommended for full-scale applications.

Modelling hydrodynamics of horizontal flow steel slag filters designed to upgrade phosphorus removal in small wastewater treatment plants

Steel slag filters, if well designed and operated, may upgrade phosphorus removal in small wastewater treatment plants such as stabilization ponds and constructed wetlands. The main objective of this study was to develop a systemic modelling approach to describe changes in the hydraulic performances and internal hydrodynamics of steel slag filters under real dynamic operating conditions. The experimental retention time distribution curves (RTD curves) determined from tracer experiments performed at different times during the first year of operation of two field-scale steel slag filters were analyzed through a three stage process. First, a statistical analysis of the RTD curves was performed to determine statistical parameters of the retention time distribution. Second, classical tanks in series (TIS) and plug flow with dispersion (PFD) models were used to obtain a first evaluation of the dispersion and mixing regime. Finally, a multi-flow path TIS model, based on the assumption of several flow paths with different hydraulic properties, is proposed to accurately describe the internal hydrodynamics. Overall, the results of this study indicate that higher CaO content, round shape, and larger grain size distribution of steel slag may promote plug-like flow rather than dispersion. The results of the multi-flow path TIS model suggest that the internal hydrodynamics of steel slag filters can be primarily described by two main flow paths: (i) a faster main flow path showing higher plug flow, followed by (ii) a slower secondary flow path showing higher dispersion. The results also showed that internal hydrodynamics may change over time as a consequence of physical-chemical phenomena occurring in the filter, including accumulation of precipitates, slag hydration and carbonation, and particle segregation.

Numerical simulations with the P-Hydroslag model to predict phosphorus removal by steel slag filters

The first version of the P-Hydroslag model for numerical simulations of steel slag filters is presented. This model main original feature is the implementation of slag exhaustion behavior, crystal growth and crystal size effect on crystal solubility, and crystal accumulation effect on slag dissolution. The model includes four mineral phases: calcite, monetite, homogeneous hydroxyapatite (constant size and solubility) and heterogeneous hydroxyapatite (increasing size and decreasing solubility). In the proposed model, slag behavior is represented by CaO dissolution kinetic rate and exhaustion equations; while slag dissolution is limited by a diffusion rate through a crystal layer. An experimental test for measurement of exhaustion equations is provided. The model was calibrated with an experimental program made of three phases. Firstly, batch tests with 300 g slag sample in synthetic solutions were conducted for the determination of exhaustion equation. Secondly, a slag filter column test fed with synthetic solution was run for 623 days, divided into 9 cells and sampled at the end of the experiment. Finally, the column was dismantled, sampled and analyzed with XRD, TEM and SEM. Experimental column curves for pH, oPO4, Ca and inorganic carbon were well predicted by the model. Crystal sizes measured by XRD and TEM validated the hypothesis for homogeneous precipitation while SEM observations validated the thin crystal layer hypothesis. A preliminary validation of the model resulted in successful predictions of a steel slag filter longevity fed with real wastewater.

Aerated steel slag filter system performance study for pollutants removal from domestic wastewater

Nitrogen removal from wastewater often requires a highly cost of chemical treatment to prevent over loading of nutrient in effluent discharge to the surface water body. However, to remove nitrogen it requires a complex process. Therefore, the aim of this study is to develop an aerated rock filter (ARF) system design under Malaysia condition. A pilot-scale VFARF with 2.0 m height and 0.3 m diameter and a HFARF with 1.0 m long and 0.3 m wide and 0.5 m height has been developed at Taman Bukit Perdana Wastewater Treatment Plant (WWTP) Batu Pahat, Johor to monitor the performance of the ARFs for nitrogen removal from domestic wastewater. The optimum value of HLR and aeration rate was 2.72 m 3 /m 3 .day and 10 L/min, respectively. For monitoring the effectiveness of the VFARF and HFARF, influent and effluent twice a week grab samples have been collected and analysed for TKN, Ammonia Nitrogen, BOD5, COD, TSS, Alkalinity, E- coli, pH, Dissolved Oxygen and Temperature. From the study, it was found that the VFARF system has outperformed as the removal efficiency of TKN, AN, TSS, and E-coli was 89%±7%, 97%±2%, 86%±17%, and 97%±2%. The removal efficiency was slightly lower in the HFARF as their removal was 78%±11%, 71%± 12%, 88%±15%, and 91%±16% for TKN, AN, TSS, and E-coli . However, their performance insignificant in removing organic matter, BOD5, COD as the removal efficiencies in the VFARF and HFARF were 84%±13%, 65%±23% and 85%±12%, 75%±21%, respectively. Alkalinity, pH and DO profiles for VFARF and HFARF systems effluent values were average at 107.08±28.35 mg/L, 7.14±0.27, 5.20±0.84 mg/L, 147.24±16.20 mg/L, 6.99±0.15 and 3.75±0.37 mg/L, respectively. Temperature value for this VFARF and HFARF system was 31.1±1.1oC. From monitoring study between VFARF and HFARF, it found that VFARF system was outperformed than the HFARF in removing nitrogen from domestic wastewater.

Comparisons Study of Phosphate Removal in Unaerated and Aerated High Calcium Steel Slag Filter System of Different pH Feed

Excess phosphorus in water body will lead to eutrophication. This study investigated the phosphate removal efficiencies of unaerated and aerated filter systems using high composition of Calcium (Ca) steel slag as the filter media at different pH values of the wastewater influents. Lab-scale filters were developed using 25 mg/L synthetic wastewater and weekly sampling was done to monitor the phosphate removal efficiencies together with the concentration of metals (Calcium (Ca) and Magnesium (Mg). The results show that both unaerated and aerated systems have excellent phosphate removal efficiency at all acidic, neutral and alkaline pH feed, though unaerated systems removed slightly better compared to aerated systems; 76-98% and 69-97% respectively. The dominant phosphate removal mechanism for aerated systems was adsorption, meanwhilefor unaerated systems; both adsorption and precipitation for acidic and neutral pH, whileprecipitation was more dominant at basic pH. The performance of unaerated systems are slightly better compared to aerated systems, however, aerated systems are recommended to be applied when simultaneous removal of nutrients (phosphorus and nitrogen) are concerned.

Treatment of fish farm sludge supernatant by aerated filter beds and steel slag filters—effect of organic loading rate

The goal of our study was to develop an on-site cost-effective and extensive method for the treatment of supernatant of the sludge settling silo of fresh water fish farms. The main objectives of this study were 1) to determine the effect of the organic loading rate (OLR) on organic matter and nutrient removal efficiency of a pilot treatment system consisting of a series of aerated filter beds (AFBs) and electric arc furnace steel slag filters operated at different void hydraulic retention times (HRTV), 2) to validate the P-Hydroslag model as a design tool for slag filters and 3) to propose preliminary design options for fish farm sludge treatment. The 11.5 month experiment was divided into two phases: Phase 1 (P1) of 8.5 months with a low OLR to the AFBs of 0.015kg BOD5m−3 d−1, and Phase 2 (P2) of 3 months with a high OLR of 0.5kg BOD5m−3 d−1. The results showed that the OLR affected the organic matter mineralization and nitrification efficiency of AFBs. With a low OLR and an influent COD concentration of 320mgL−1, an average COD removal efficiency of 95% was observed while with a high OLR and an influent COD of 5400mgL−1, an average COD reduction of 65% was achieved. Due to the high OLR during P2, no nitrification took place probably due to the low availability of oxygen in the AFBs. The TP removal efficiency of the AFBs was 50% during P1 (influent of 5.2mgL−1), and 88% during P2 (influent of 110mgL−1). All SCs showed a high o-PO4 removal efficiency of >98% during P1 (average influent of 1.8mg P L−1, effluent of 0.04mg P L−1) and >85% during P2 (average influent of 8.7mg P L−1, effluent of 0.65mg P L−1) with a decrease in efficiency only observed over time in the SC that received the highest organic loading rate. It was concluded that with optimal loading rates, this compact biological and physicochemical semi-extensive treatment system offers a promising alternative to the high energy demand and maintenance treatment systems for organic matter and phosphorus removal, and that this treatment system could be applicable to other agro-environmental, municipal or residential effluents.