Eco-friendly concrete incorporating palm oil fuel ash: Fresh and mechanical properties with machine learning prediction, and sustainability assessment

Rising natural resource consumption leads to increased hazardous gas emissions, necessitating the concrete industry's focus on sustainable alternatives like palm oil fuel ash (POFA) to replace cement. Also, advanced machine learning (ML) techniques can uncover previously unreported insights about the effects of POFA that may be missing from the literature. Hence, this study investigates the influence of varying concentrations of POFA on fresh and mechanical characteristics with quantifying ML approaches and microstructural performance, as well as the environmental impact of structural concrete. For this, cement substitutions of 5 %, 15 %, 25 %, 35 %, and 45 % (by weight of cement) were utilized. POFA enhanced the overall concrete workability, with slump increments ranging from approximately 9 %-55 % and compacting factor increments of 4 %-12 %. Mechanical performance of POFA concrete improved up to 25 % replacement levels, with the highest enhancements observed in compressive (4.5 %), splitting tensile (36 %), and flexural (31 %) strength, for the mix containing 15 % POFA. The finer particle size of POFA improved microstructural performance by reducing porosity, aligning with the enhanced mechanical strength. The environmental impact of POFA was assessed by measuring eCO2 emissions, revealing a potential reduction of up to 44 %. Incorporating 5 %-15 % POFA yielded ideal mechanical performance results, significantly enhancing sustainability and cost-effectiveness. Regarding the ML approach, it can be observed that a low regression coefficient (R2) contrasts sharply with the higher R2 values for the random forest (RF) and the ensemble model, indicating satisfactory precision prediction with experimental results.

Influence of aeration, plants, electrodes, and pollutant loads on treatment performance of constructed wetlands: A comprehensive study with septage

This study reports the performance of non-aerated and aerated unplanted, planted, microbial fuel cell planted wetlands for stabilizing septage and treating the drained wastewater. The wetland systems of this study were dosed with septage for a relatively shorter period, i.e., 20 weeks, followed by 60 days of sludge drying period. The sludge loading rates across the constructed wetlands ranged between 259 and 624 kg total solids (TS)/m² per year. Organic matter, nitrogen, and phosphorus concentration of the residual sludge ranged between 8512 and 66,374 mg/kg, 12,950 and 14,050 mg/kg, 4979 and 9129 mg/kg, respectively. The presence of plants, electrode, and aeration improved sludge dewatering and decreased the organic matter and nutrient concentration of the residual sludge. The heavy metals (Cd, Cr, Cu, Fe, Pb, Mn, Ni, and Zn) concentration of the residual sludge fulfilled the guidelines for agricultural reuse in Bangladesh. Chemical oxygen demand (COD), ammoniacal nitrogen (NH₄-N), total nitrogen (TN), total phosphorus (TP), and coliform removal percentages from the drained wastewater ranged between 91 and 93 %, 88 and 98 %, 90 and 99 %, 92 and 100 %, and 75 and 90 %, respectively. NH₄-N removal from the drained wastewater depended upon aeration. The sludge treatment wetlands achieved metals removal percentages (from the drained wastewater) ranging between 90 and 99 %. Physicochemical and microbial routes in accumulated sludge, rhizosphere, and media contributed to pollutants removal. Input load and organic removal increment (from the drained wastewater) were positively correlated; nutrient removal showed a contradictory trend. The non-aerated and aerated microbial fuel cell planted wetlands produced maximum power densities ranging between 66 and 3417 mW/m³. Because of the shorter experimental duration, this study revealed preliminary but new information on the macro and micro pollutants removal pathways in septage sludge wetlands (with and without electrode) that could be utilized to design pilot or full-scale systems.

Organic media-based two-stage traditional and electrode-integrated tidal flow wetlands to treat landfill leachate: Influence of aeration strategy and plants

Landfill leachate treatment employing normal and electrode-integrated constructed wetlands is difficult due to the presence of significant amounts of organic compounds, which frequently impede the progression of microbial-based aerobic pollutant removal pathways. As a result, this study examines the effect of supplementary air availability via intermittent and continuous aeration strategies in improving organic, nutrient, and coliform removals of the unplanted, planted (normal and electrode-integrated) two-stage tidal flow constructed wetlands designed to treat landfill leachate. The constructed wetlands were filled with coal and biochar media and planted with Canna indica. Mean chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and coliform removal percentages of the externally aerated two-stage unplanted, only planted, planted-microbial fuel cell integrated constructed wetland systems ranged between 96 and 99%, 82 and 93%, 91 and 98%, 86 and 96%, respectively, throughout the experimental campaign. External aeration inhibited the development of a dominant anaerobic environment within the media of the wetland systems and improved overall pollutant removal. The electrode-integrated planted tidal flow wetlands produced better effluent quality than the unplanted or only planted tidal flow systems without electrode assistance. The first stages of the three wetland systems achieved an additional 5-7% COD, 7-12% TN, and 15-22% coliform removal during the continuous aeration period compared to the corresponding performance of the intermittent aeration phase. The pollutant removal performance of the second-stage wetlands decreased during the continuous aeration phase. The media composition supported electrochemically active and inactive microbial-based pollutant removal routes and the chemical adsorption of pollutants. Nitrogen and phosphorus accumulation percentage in plant tissues was low, i.e., 0.4-2.2% and 0.04-0.8%, respectively. During the continuous aeration period, the electrode-integrated tidal flow constructed wetlands achieved higher power density production, i.e., between 859 and 1432 mW (mW)/meter³(m³). This study demonstrates that external aeration might improve pollutant removal performance of the normal, electrodes integrated tidal flow-based constructed wetlands when employed for high organic-strength wastewater treatment such as landfill leachate.

Performance assessment of normal and electrode-assisted floating wetlands: influence of input pollutant loads, surface area, and positioning of anode electrodes

This study reports the design and development of microbial fuel cell (MFC) assisted floating wetlands and compares treatment removal performance with a normal (without electrodes) floating wetland. Both types of floating wetlands were planted with Phragmites plant and evaluated for real municipal wastewater treatment. The effective volume of each floating wetland was 0.5 m³. The floating wetlands were operated under variable hydraulic load rates, i.e., 20 and 60 mm/day. Mean 5-day biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), ammoniacal nitrogen (NH₄-N), total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS), and coliform removal percentages ranged between 71 and 96%, 72 and 94%, 62 and 86%, 58 and 75%, 82 and 97%, 64 and 92%, and 72 and 93%, respectively within the normal and electrode-assisted MFC integrated floating wetlands. The electrode-integrated floating wetlands showed better pollutant removal performance than the normal system under unstable input pollutant loading conditions. Nitrogen and organic matter removals were achieved through both electrochemically active and inactive microbial removal routes. Physical separation processes, such as filtration and sedimentation, contributed to phosphorus, solids, and coliform removal. Plant uptake contributed to micro-scale nitrogen (≤ 1%) and phosphorus (≤ 0.1%) removal. Increment of hydraulic/pollutant load improved organic removal but decreased nutrient removal performance of the normal, electrode-integrated floating wetlands. The electrode-integrated floating wetlands produced power densities ranging between 0.7 and 1.4 mW/m³, and 0.2 and 2.3 mW/m³ during lower, upper input loading ranges, respectively. Bioenergy production of the electrode-integrated floating wetlands varied within the two operational periods due to a wider range of electrochemically inactive microbial populations in real wastewater that interfered with electrochemical organic matter oxidation. The positioning difference of the anode electrodes was a significant factor that improved pollutant removal within the electrode-integrated floating wetlands compared to the other variable, i.e., anode electrodes surface area.

A comparative landfill leachate treatment performance in normal and electrodes integrated hybrid constructed wetlands under unstable pollutant loadings

This study provides a comparative pollutant removal performance assessment between organic or construction materials-based four hybrid wetland systems that received landfill leachate. The hybrid systems included vertical flow (VF) followed by horizontal flow (HF)-based unplanted and planted systems, and planted electrodes incorporated microbial fuel cell (MFC) integrated hybrid wetlands systems. All the systems were run in free-draining mode. Overall mean chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) removal percentage of the hybrid systems ranged between 81 and 99%, 82 and 96%, 74 and 99%, respectively, under unstable input pollutant loading conditions. Additionally, up to 27% organic and up to 14% nitrogen removal improvement was observed in electrodes integrated free-draining VF wetlands. Free-draining and additional oxygen availability from atmospheric diffusion, rootzone improved the removal performance of MFC-based VF wetlands. Input load increment decreased organic, nutrient removals in second stage HF units due to saturated media. The chemical composition of the employed media supported biotic, abiotic organic, nutrient removal pathways. Nutrient accumulation percentage in plants tissue was very low, i.e., ≤3%. Bioenergy production across the MFC-based VF-HF wetlands decreased with input pollutant load increment. The single anode electrode-based VF wetland achieved maximum power density production, i.e., 294 mW/m².. The electrodes integrated hybrid systems achieved comparatively stable removal performance despite input pollutant/hydraulic load variation.

Development of electrodes integrated hybrid constructed wetlands using organic, construction, and rejected materials as filter media: Landfill leachate treatment

This study developed microbial fuel cell (MFC)-based hybrid constructed wetland systems using different filter media, i.e., organic (biochar), construction (sand), and rejected (iron particle, concrete particle, and stone dust) materials, and evaluated the performance of the developed systems for treating landfill leachate. The mean ammonium nitrogen (NH₄-N), total nitrogen (TN), total phosphorus (TP), biochemical oxygen demand (BOD), chemical oxygen demand (COD) removal percentages within the hybrid systems ranged between 91 and 98%, 90 and 98%, 97 and 99%, 88 and 93%, 93 and 97%, respectively, despite higher pollutants concentration in leachate wastewater. The aerobic environment in the cathode compartment (due to intermittent load) and free-draining of wastewater (from cathode to anode compartment) supported electrochemically inactive, active pollutants removal in the electrodes integrated first stage vertical flow (VF) wetlands. The second stage electrodes integrated horizontal flow (HF) wetlands supported electrochemical-based organic removal and nitrification because of efficient organic removal in the previous VF wetland stages. Nitrogen, phosphorus accumulation percentages in plant tissues ranged between 0.3 and 7%, 0.4 and 14%, respectively. Nutrient removal was achieved through chemical and microbial routes. The biochar-packed VF wetland produced a maximum power density of 20.6 mW/m². The coexistence of unsaturated, saturated media in the partially saturated HF wetland maintained the required environmental gradient between the electrodes and improved operational performance.

Intensified constructed wetlands for the treatment of municipal wastewater: experimental investigation and kinetic modelling

This study reports organics and nutrient removal performances of the intensified constructed wetlands, i.e., tidal flow-based microbial fuel cell (MFC) and tidal flow wetlands that received municipal wastewater. The wetland systems were filled with organic (coco peat, biochar) or waste (Jhama brick, steel slag) materials, planted with Phragmites australis or Chrysopogon zizanioides (Vetiver) species, and operated under three flood periods: 8, 16, 24 h. Input ammonia nitrogen (NH3-N), total nitrogen (TN), phosphorus (P), chemical oxygen demand (COD), and biochemical oxygen demand (BOD) load across the wetland systems ranged between 3-27, 12-78, 0.1-23, 36-1130, and 11-281 g/m2day, respectively; mean removal percentages were 60-83, 74-84, 95-100, 94-98, and 93-97%, respectively, throughout the experimental run. The wetland systems achieved similar organics and P removals; operational and media variation did not influence removal kinetics. All wetland systems achieved the highest TN removal (76-87%) when subjected to 24-h flood period. TN removal performances of waste material-based wetlands were comparable to organic media-based systems. Tidal flow-based MFC wetlands achieved better TN removal than tidal flow wetlands because of supplementary electron production through fuel cell-based organics degradation kinetics. Maximum power production rates across the tidal flow-based MFC wetlands ranged between 53 and 57 mW/m2. Monod kinetics-based continuous stirred tank reactor (CSTR) models predicted NH3-N, TN, and COD removals (in wetland systems) more accurately. Kinetic models confirmed the influence of substrate (i.e., pollutant) and environmental parameters on pollutant removal routes.

Strength Properties of Sustainable Mortar Containing Waste Steel Slag and Waste Clay Brick: Effect of Temperature

The use of waste streams for the production of sustainable cement-based materials cannot be overemphasized. This study investigates the feasibility of reusing waste steel slag (WSS) and waste clay brick (WCB) as a replacement for natural sand (NS) in mortar. Numerous studies have reported mainly the compressive strength of concrete/mortar, while limited research is available that focuses on the tensile and flexural strength of mortar, and especially the performance at elevated temperature. Hence, this study investigates the tensile and flexural strength of mortar with three different replacement percentages (0, 50 and 100% by volume of NS) of NS by WSS and WCB at normal temperature (without thermal treatment) and after exposure to elevated temperatures (250, 400 and 600 °C). At ambient condition, both tensile and flexural strength were enhanced as the WSS content increased (76 and 68%, respectively, at 100% WSS). In comparison, the strength increased at 50% WCB (25 and 37%, accordingly) and decreased at 100% WCB (23 and 20%, respectively) compared to 100% NS. At elevated temperatures, both the tensile and flexural strength of mortar mixes decreased significantly at 600 °C.

Shear Response of Glass Fibre Reinforced Polymer (GFRP) Built-Up Hollow and Lightweight Concrete Filled Beams: An Experimental and Numerical Study

This paper investigated the static behaviour of glass fibre reinforced polymer (GFRP) built-up hollow and concrete filled built-up beams tested under four-point bending with a span-to-depth ratio of 1.67, therefore focusing their shear performance. Two parameters considered for hollow sections were longitudinal web stiffener and strengthening at the web–flange junction. The experimental results indicated that the GFRP hollow beams failed by web crushing at supports; therefore, the longitudinal web stiffener has an insignificant effect on improving the maximum load. Strengthening web–flange junctions using rectangular hollow sections increased the maximum load by 47%. Concrete infill could effectively prevent the web crushing, and it demonstrated the highest load increment of 162%. The concrete filled GFRP composite beam failed by diagonal tension in the lightweight concrete core. The finite element models adopting Hashin damage criteria yielded are in good agreement with the experimental results in terms of maximum load and failure mode. Based on the numerical study, the longitudinal web stiffener could prevent the web buckling of the slender GFRP beam and improved the maximum load by 136%. The maximum load may be further improved by increasing the thickness of the GFRP section and the size of rectangular hollow sections used for strengthening. It was found that the bond–slip at the concrete–GFRP interface affected the shear resistance of concrete–GFRP composite beam.

Pollutant removal from landfill leachate employing two-stage constructed wetland mesocosms: co-treatment with municipal sewage

Constructed wetlands are low-cost, natural technologies that are often employed for the treatment of different types of wastewater. In this study, landfill leachate and municipal wastewater were co-treated by the three parallel two-stage Phragmites- or Vetiver-based constructed wetland mesocosms. Two-stage wetland mesocosms included vertical flow (VF) units as the first stage, followed by horizontal flow (HF)/surface flow (SF)/floating treatment (FT) units. VF and HF wetland mesocosms were filled with gravel, steel slag, concrete block, and intermittent carbon-saturated ceramic filters as substrates. Mean input nitrogen, organics, and phosphorus load across first stages were 75 g N/m² day, 283 g COD/m² day, 88 g BOD/m² day, and 10 g P/m² day, respectively. N and P accumulation rate was not substantial (< 10%) with respect to total removal in most wetland mesocosms. Gravel-based VF wetland mesocosm achieved better NH₄-N and BOD removal (55-59%) during landfill leachate treatment phase, when compared with co-treatment periods (12-52%). Slag-concrete- and ceramic filter-based VF wetland mesocosms maintained stable NH₄-N and BOD removals; the former wetland mesocosm was the most efficient VF unit (than other two wetland mesocosms) due to media characteristics. Media-based adsorption accelerated P removal (93%) in slag-concrete-based VF wetland mesocosm. Carbon scarcity limited denitrification in all VF wetland mesocosms; removal of TN was < 32%. Second stage wetland mesocosms achieved higher nitrogen (85-92%), organics (66-90%), and phosphorus (97-100%) removals regardless of operational variations; low input load, long retention time, media, and rhizosphere enhanced removal performances, particularly in HF and FT wetland mesocosms. In general, this study demonstrates potential application of two-stage wetland mesocosms for landfill leachate treatment or co-treatment with municipal sewage.

Enhancement of Mechanical Properties and Porosity of Concrete Using Steel Slag Coarse Aggregate

This paper investigates the possibility of utilizing steel slags produced in the steelmaking industry as an alternative to burnt clay brick aggregate (BA) in concrete. Within this context, physical, mechanical (i.e., compressive and splitting tensile strength), length change, and durability (porosity) tests were conducted on concrete made with nine different percentage replacements (0%, 10%, 20%, 30%, 40%, 50%, 60%, 80%, and 100% by volume of BA) of BA by induction of furnace steel slag aggregate (SSA). In addition, the chemical composition of aggregate through X-ray fluorescence (XRF) analysis and microstructural analysis through scanning electron microscopy (SEM) of aggregates and concrete were performed. The experimental results show that the physical and mechanical properties of concrete made with SSA were significantly higher than that of concrete made with BA. The compressive and tensile strength increased by 73% when SSA fully replaced BA. The expansion of concrete made with SSA was a bit higher than the concrete made with BA. Furthermore, a significant lower porosity was observed for concrete made with SSA than BA, which decreased by 40% for 100% SSA concrete than 100% BA concrete. The relation between compressive and tensile strength with the porosity of concrete mixes are in agreement with the relationships presented in the literature. This study demonstrates that SSA can be used as a full replacement of BA, which is economical, conserves the natural aggregate, and is sustainable building material since burning brick produces a lot of CO₂.

Effect of Recycled Iron Powder as Fine Aggregate on the Mechanical, Durability, and High Temperature Behavior of Mortars

This study evaluates the mechanical, durability, and residual compressive strength (after being exposed to 20, 120, 250, 400 and 600 °C) of mortar that uses recycled iron powder (RIP) as a fine aggregate. Within this context, mechanical strength, shrinkage, durability, and residual strength tests were performed on mortar made with seven different percentages (0%, 5%, 10%, 15%, 20%, 30% and 50%) of replacement of natural sand (NS) by RIP. It was found that the mechanical strength of mortar increased when replaced with up to 30% NS by RIP. In addition, the increase was 30% for compressive, 18% for tensile, and 47% for flexural strength at 28 days, respectively, compared to the reference mortar (mortar made with 100% NS). Shrinkage was observed for the mortar made with 100% NS, while both shrinkage and expansion occurred in the mortar made with RIP, especially for RIP higher than 5%. Furthermore, significantly lower porosity and capillary water absorption were observed for mortar made with up to 30% RIP, compared to that made with 100% NS, which decreased by 36% for porosity and 48% for water absorption. As the temperature increased, the strength decreased for all mixes, and the drop was more pronounced for the temperatures above 250 °C and 50% RIP. This study demonstrates that up to 30% RIP can be utilized as a fine aggregate in mortar due to its better mechanical and durability performances.