Ageing of HDPE geomembrane exposed to air,water and leachate at different temperatures

The latest findings regarding the long-term performance and service life of HDPE geomembrane (GM) samples exposed to air, water and leachate are presented based on data from samples that have been ageing for 8–10 years. Some of the GM samples are in Stage II, some in Stage III and some have completed all three stages of the service life. The paper provides: (1) improved data on antioxidant depletion rates for GMs immersed in air, water and leachate; (2) estimates of antioxidant depletion time (Stage I) at typical liner temperatures in air, water and leachate and, based on this data, an estimate for a composite liner at typical liner temperatures; (3) data regarding the changes in the physical and mechanical properties of the GM samples with time; (4) a surface analysis of virgin and aged GMs; (5) an initial estimate of the induction time (Stage II) and polymer degradation time (Stage III) and service lives of GM in laboratory immersion tests; and (6) predictions of the service life of leachate immersed GM at typical landfill temperatures. Based on these predictions, it appears likely that the service life of the specific GM tested immersed in leachate is likely to exceed 700 years and will probably be of the order of 1000 years (or longer) at 20 °C, more than 150 years and likely 225–375 years at 35 °C and more than 40 years and likely 50–90 years at 50 °C. The service life in a liner configuration may be expected to be longer than predicted here for immersion in leachate.     

Effect of high temperatures on antioxidant depletion from different HDPE geomembranes

The effect of elevated temperatures, typically 95–115 °C, on antioxidant depletion from a high-density polyethylene (HDPE) geomembrane (GMB) incubated in air, water and synthetic leachate is examined. It is shown that the antioxidant depletion in synthetic leachate at 95–115 °C is consistent with what would be expected from Arrhenius modeling based on data from lower temperatures (25–85 °C). A similar finding is reached for incubation in air. However, when incubated in water the antioxidant depletion is more complicated. At temperatures above 100 °C a four-parameter exponential model was needed to fit oxidative induction time data that exhibited quite different early-time and later-time depletion rates. The early-time depletion rate decreases with an increase of the temperature while the later-time depletion rates follow the more typical pattern of increasing with increasing temperature. Three additional HDPE GMBs with different antioxidant packages are examined at elevated temperatures in air. The GMB with the lowest initial standard (Std) oxidative induction time (OIT) and without hindered amine light stabilizer (HALS) has the longest antioxidant depletion stage based on Std-OIT at these elevated temperatures. GMBs stabilized with HALS showed only a slight change in their high pressure OIT during the current study. It is shown also that degradation in physical properties can start at Std-OIT values above the residual OIT values.     

Predicting the depletion of antioxidants in high density polyethylene (HDPE) under sunlight using the reciprocity law

Depletion of antioxidants in HDPE subjected to sunlight exposure was studied. Sunlight radiation was simulated using a laboratory xenon light weatherometer at three irradiation levels. Oxidative induction time (OIT) test was performed on different layers along the thickness of the test coupons to establish the antioxidant depletion throughout the exposure duration. The highest drop in OIT was obtained for the surface layer facing the radiation, followed by the backside layer which was exposed to indirect radiation reflected from the wall of the weatherometer. The core section showed a slower decrease under the same exposure conditions. Furthermore, the OIT depletion rate in the surface layer increased with radiation intensity. The study proved that the sunlight degradation of the tested polyethylene can be accelerated by increasing the irradiation intensity based on the reciprocity law.     

Durability of fluorinated high density polyethylene geomembrane in the Arctic

A series of fluorinated high density polyethylene (f-HDPE) geomembrane (GM) samples of different thickness (1, 1.5 and 2.5 mm) was exhumed from the backfill immediately upstream of a barrier system constructed to contain a hydrocarbon spill in the Canadian Arctic. The samples were tested for oxidation induction time (OIT), crystallinity, melt index (MI) and tensile properties. The results of these tests are reported and it is shown that the durability of the GM was maintained well beyond the initial 3-year design life of the barrier system. Based on 7 years of field data, the std-OIT depletion time for the 1.5 mm thick GM used in the barrier system was inferred to be over 140 years while the antioxidant depletion time based on the HP-OIT is estimated to be about 200 years. No significant temporal changes in the crystallinity, MI or tensile properties of the exhumed GM samples were detected.     

Interaction of antioxidants with carbon black in polyethylene using oxidative induction time methods

Carbon black (CB) is added to the geosynthetics for ultraviolet protection. However, CB can interact with antioxidant (AO) in the geosynthetics, and their interaction has been documented to be synergistic and/or antagonistic towards the oxidation reaction. In this paper, two oxidative induction time (OIT) methods, a standard (Std) OIT test and a high pressure (HP) OIT test, were used to evaluate the interaction of CB with two types of antioxidants during the oven aging. Test samples made from high density polyethylene (HDPE) blended with different amounts of Irganox^®1010 (I-1010) and Irgafos^®168 (I-168) together with 0 or 2.5wt.% of carbon black were studied. The sample were incubated in a forced air oven at 85 °C to accelerate the oxidation reactions. After 1000 days, Std-OIT values of samples with 500 ppm and 1000 ppm I-1010 exhibited only 10% drop from their initial values from 19.42 min and 34.01 min to 17.53 and 31.0 min respectively. In comparison, a continuous decrease of Std-OIT value was observed for samples contained both I-1010 and I-168; a 40% drop was measured after 1000 days, corresponding to 16.4 and 26.8 min reduction. For samples contained 2.5% CB and I-1010, an exponentially decrease of Std-OIT and HP-OIT with aging time was obtained. However, adding I-168 to those samples did not change the OIT decreasing trends, indicating that the interaction of CB with I-168 is negligible. The test data further verify that the effectiveness of the OIT test is strongly correlated to the functional temperature range of the AO. The Std-OIT test with testing temperature of 200 °C can detect both I-1010 and I-168, while the 150 °C testing temperature of the HP-OIT test can only detect the I-1010.     

Geomembrane strains from coarse gravel and wrinkles in a GM/GCL composite liner

The physical response of a 1.5-mm-thick, high-density polyethylene geomembrane (GM) is reported when placed on top of a needle-punched geosynthetic clay liner (GCL), buried beneath 50-mm coarse gravel and subjected to vertical pressure in laboratory experiments. Local strains in the geomembrane caused by indentations from the overlying gravel and deflections of a wrinkle in the geomembrane are quantified. A peak strain of 20% was calculated when a flat geomembrane was tested without a protection layer at an applied vertical pressure of 250 kPa. Strains were smaller with a nonwoven needle-punched geotextile protection layer between the gravel and geomembrane. Increasing the mass per unit area of the geotextile up to 2200 g/m² reduced the geomembrane strain. However, none of the geotextiles tested were sufficient to reduce the geomembrane strain below an allowable limit of 3%, for the particular 50-mm gravel tested and when subjected to a vertical pressure of 250 kPa. Increasing the initial GCL water content and reducing the stiffness of the foundation layer beneath the GCL were found to increase the geomembrane strains. These local strains were greater when a wrinkle was present in the geomembrane. The wrinkle in the geomembrane experienced a decrease in height and width. The wrinkle deformations lead to larger pressures beside the wrinkle and hence producing larger local strains. A 150-mm-thick sand protection layer was effective in limiting the peak strain to less than 0.3% even with a wrinkle in the geomembrane, at a vertical pressure of 250 kPa.     

Technetium-99 (Tc) in annual growth segments of knotted wrack (Ascophyllum nodosum)

The distribution of technetium-99 (⁹⁹Tc) in annual growth segments of the brown seaweed Ascophyllum nodosum (Fucales, Phaeophyceae) from the southwestern coast of Norway is examined in samples collected from January to November 2006. A twenty-fold increase in the ⁹⁹Tc-concentration from the youngest to the oldest growth segments was found. The concentrations ranged from 42 to 98 Bq/kg dry weight (d.w.) and from 964 to 1000 Bq/kg d.w. in growth segments formed in 2006 and 1996, respectively. In addition, a seasonal variation in the ⁹⁹Tc concentration was observed in the actively growing 2006-segments: concentrations decreased from 98 Bq/kg d.w. in April to 54 Bq/kg d.w. in June; there was a further reduction from June to August (42 Bq/kg d.w.); and, finally there was an increase from August to November (93 Bq/kg d.w.). In most of the segments formed between 2000 and 2005, there was a tendency of slightly decreasing ⁹⁹Tc-concentrations between June and November but this pattern was not observed for the older growth segments. In order to find an explanation for the non-homogenous distribution of ⁹⁹Tc within thalli of A. nodosum, different hypotheses are discussed. Uptake and elimination of ⁹⁹Tc appears to be most pronounced in the actively growing segments. To date, such non-homogenous distribution of ⁹⁹Tc within thalli of A. nodosum has not been taken into consideration, neither in connection with sample collection nor analysis. This paper shows that special protocols must be followed if A. nodosum is going to be used as a bioindicator for ⁹⁹Tc in the marine environment. A sampling strategy is proposed.     

Long-term Performance of Conductive-backed multilayered HDPE Geomembranes

The long-term performance of three multilayered textured white conductive-backed geomembranes (GMBs) is compared to the comparable textured nonconductive GMBs and their smooth edge/equivalent to investigate the effect of the conductive layer on their longevity. Oven immersion in synthetic municipal solid waste leachate is used at a range of temperatures to accelerate the ageing during an incubation period of 50 months. It is shown that the conductive layer can antagonistically or synergistically affect the antioxidant depletion of conductive-backed GMBs relative to nonconductive GMBs produced by the same GMB manufacturer and formulated using the same nominal resin and antioxidant package. However, their relative degradation at 85 °C does not necessarily follow their relative antioxidant depletion times implying that the manufacturing process and the interaction between the additive packages of these GMBs can affect their relative degradation beyond the antioxidant depletion stage. Arrhenius modelling predicts the antioxidant depletion stage at field temperatures ranging between 180 and 1400 years at 20 °C for two different conductive-backed GMBs produced by two different manufacturers. With such variation in the long-term performance of conductive-backed GMBs currently available in the market, their durability should be investigated before their use in barrier systems to ensure they can meet the required design life of the desired geoenvironmental application.     

Antioxidant depletion from five geomembranes of same resin but of different thicknesses immersed in leachate

The effect of thickness on the antioxidants depletion time for five high density polyethylene geomembranes (with nominal thicknesses of 0.5, 1.0, 1.5, 2.0, and 2.4 mm) immersed in synthetic leachate at six different temperatures (25, 40, 55, 70, 85 and 95 °C) is investigated. The geomembranes were manufactured from the same geomembrane resin (i.e., polymer resin, antioxidant/stabilizer package, and carbon-black batch). Four (1.0, 1.5, 2.0, and 2.4 mm) of the five geomembranes were manufactured during the same production run by changing the pulling speed of the geomembrane from the extrusion die. The depletion of antioxidants/stabilizers inferred from both standard (Std-) and high pressure (HP-) oxidative induction times (OIT)s show that increasing geomembrane thickness resulted in longer depletion times for temperatures above 40 °C but little to negligible difference in projected depletion times below 40 °C for this antioxidant package. The increase in depletion times was not proportional to the square of the geomembrane thickness as theoretically predicted if depletion was diffusion controlled and the diffusion coefficient was the same for each GMB. Thus, the depletion of antioxidants is not fully governed by diffusion and/or the GMB's diffusion coefficients are different. Regardless of the GMB thickness, the time for Std-OIT depletion was shorter than the time to residual HP-OIT above 70 °C but was longer at or below 55 °C. For example, for 2.4 mm GMB, the inferred time for Std-OIT depletion was 0.2–0.3 (at 85 °C), 2–3.5 (at 55 °C) and 9.5 (at 40 °C) times that for the HP-OIT to deplete to residual. The projected Std-OIT depletion times for 1.0 and 2.4 mm GMBs were: 2.7 and 4 years, respectively, at 60 °C; 23 and 26 years, respectively, at 40 °C; and about 330 years at 20 °C.     

Convolutional variational autoencoder for ground motion classification and generation toward efficient seismic fragility assessment

This study develops an end-to-end deep learning framework to learn and analyze ground motions (GMs) through their latent features, and achieve reliable GM classification, selection, and generation of simulated motions. The framework is composed of an analysis workflow that transforms and reconstructs GMs through short-time Fourier transform (STFT), encodes and decodes their latent features through convolutional variational autoencoder (CVAE), and classifies and generates GMs by grouping and interpolating latent variables. A benchmark study is established to confirm the minor difference between original GMs and the corresponding reconstructed accelerograms. The encoded latent space reveals that certain latent variables are directly linked to the dominant physical features of GMs. Resultantly, clustering latent variables using the k-means algorithm successfully classifies GMs into different groups that vary in earthquake magnitude, soil type, field distance, and fault mechanism. By linearly interpolating two parent latent variables, simulated GMs are generated with consistent class information and matching response spectra. Furthermore, seismic fragility models are developed for a steel frame building and a concrete bridge using different sets of GMs. Using five classified, top-ranked motions, regardless of recorded or simulated accelerograms, can achieve reasonable and efficient fragility estimates compared to the case that adopts 230 GMs. The proposed deep learning framework addresses two compelling questions regarding seismic fragility assessment: How many GMs are sufficient and what types of motions should be selected.     

Isothiazolone emissions from building products

Adding biocides to dispersion products is a well‐known practice to control microbial deterioration. Isothiazolones are among the most commonly used preservatives, in particular a mixture of 2‐methyl‐2H‐isothiazol‐3‐one (MIT) and 5‐chloro‐2‐methyl‐2H‐isothiazol‐3‐one (CIT). In recent years, for health reasons, due to its strong sensitizing effect, CIT has been replaced by 1,2‐benzisothiazol‐3‐one (BIT). Furthermore, numerous products are now available for interiors containing the fungicidal active substance 2‐octyl‐2H‐isothiazol‐3‐one (OIT). So far nearly nothing is known of the emission behavior of BIT and OIT. An analytical method was developed for these two isothiazolones and interior products containing BIT respectively OIT have been investigated in an emission chamber and in test rooms. The chamber tests revealed maximum concentrations of 6.7 μg OIT/m³, 1.9 μg BIT/m³, and 187 μg MIT/m³. Concentrations obtained in the test rooms were at levels up to 1.4 μg OIT/m³ and 29 μg MIT/m³. A noticeable finding was the very slight subsidence of OIT and BIT levels over several weeks. While MIT outgassed quickly, OIT in particular showed low concentrations, but prolonged evaporation.     

Migration behavior of landfill leachate contaminants through alternative composite liners

Four identical pilot-scale landfill reactors with different alternative composite liners were simultaneously operated for a period of about 540 days to investigate and to simulate the migration behaviors of phenolic compounds (phenol, 2-CP, 2-MP, 3-MP, 4-MP, 2-NP, 4-NP, 2,4-DNP, 2,4-DCP, 2,6-DCP, 2,4,5-TCP, 2,4,6-TCP, 2,3,4,6-TeCP, PCP) and heavy metals (Pb, Cu, Zn, Cr, Cd, Ni) from landfill leachate to the groundwater. Alternative landfill liners of four reactors consist of R1: Compacted clay liner (10 cm + 10 cm, k = 10⁻⁸ m/sn), R2: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm + 10 cm, k = 10⁻⁸ m/sn), R3: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn) + bentonite liner (2 cm) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn), and R4: Geomembrane (2 mm HDPE) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn) + zeolite liner (2 cm) + compacted clay liner (10 cm, k = 10⁻⁸ m/sn). Wastes representing Istanbul municipal solid wastes were disposed in the reactors. To represent bioreactor landfills, reactors were operated by leachate recirculation. To monitor and control anaerobic degradation in the reactors, variations of conventional parameters (pH, alkalinity, chloride, conductivity, COD, TOC, TKN, ammonia and alcaly metals) were also investigated in landfill leachate samples. The results of this study showed that about 35-50% of migration of organic contaminants (phenolic compounds) and 55-100% of migration of inorganic contaminants (heavy metals) to the model groundwater could be effectively reduced with the use of bentonite and zeolite materials in landfill liner systems. Although leachate contaminants can reach to the groundwater in trace concentrations, findings of this study concluded that the release of these compounds from landfill leachate to the groundwater may potentially be of an important environmental concern based on the experimental findings.     

Application of Codes Performance‐Based Design Procedures for a Tall Building Using Recorded and Spectrally Modified Ground Motions

There is a growing tendency toward the performance‐based design of tall buildings, where any assessment using response history analysis requires a set of ground motion (GM) records. This paper considering a tall building as a case study investigates how judgment on the seismic safety of the structure is affected by the use of recorded or spectrally matched GMs. Three model structures are developed: (a) using conventional design procedure of Chapter 12 of ASCE 7‐16; (b) adopting linear analysis requirements of Chapter 16 of ASCE 7‐16; (c) designing for service‐level design earthquake of Los Angles Tall Building Structural Design Council (LATBSDC) procedure. It is shown that all of the structures give acceptable performance when subjected to simulated GMs, although this is not the case for amplitude‐scaled GMs based on ASCE 7‐16 and LATBSDC. Finally, to have an objective assessment of performance, independent of GM types, incremental dynamic analysis is employed to derive fragility and mean annual rate of exceeding (MAR). Results show that for anticipated drifts at Maximum Considered Earthquake (MCE) level, the structures provide acceptable MAR at the fundamental period. However, for the higher modes including the second and third periods, MAR values become acceptable only at drifts as large as 0.085.     

Biological treatment at low temperatures of sulfur-rich phenols containing oil shale ash leachate

Aerobic and sequential anaerobic-aerobic treatment of oil shale ash dump leachate (COD 2000–3000 mg l⁻¹) was studied at 7–10° and at 20°C. The leachate was known to contain several phenolic compounds and have a high sulfur concentration. In the sequential anaerobic-aerobic processes, the chemical oxygen demand (COD) removals were most of the time slightly lower at 10°C (67%) than at 20°C (73%) while the biochemical oxygen demand for 7 days (BOD₇) removals were 97–99% at both temperatures. In the anaerobic stages, the COD removal was a result of sulfide production. In the single aerobic process at 20°C, the COD removal was 65% while at 7°C the COD removal was 54%. After the feed was changed from leachate to phenol in the 7°C aerobic reactor, the COD removal stabilized to about 95%. In all the leachate treatment processes studied, the total phenols removals were on average 78–86%. The anaerobic stages removed total phenols minimally. An aerobic process at 7–20°C alone seems feasible for treating oil shale ash leachate.     

Assessment of HDPE geomembrane performance in a municipal waste landfill double liner system after eight years of service

In the late 1970s and early 1980s, environmental regulations were upgraded in a general national movement to effect secure management of our municipal and residual solid wastes. The new regulations required varying combinations of natural and/or synthetic barrier and drainage layers to prevent the unrestricted release of contaminants.

The acceptable barrier materials included synthetic flexible membrane liners (FMLs) of various types. One of those most commonly used has been high-density polyethylene (HDPE) geomembrane. HDPE has been selected because of its good chemical resistance characteristics, among others. Background compatibility testing has shown the HDPE geomembrane to be extremely resistant to the leachates that are generated by municipal and residual solid waste landfills. The background testing for design has generally been based on relatively short-term tests that are conducted under extreme conditions to ‘forecast’ service life.

Recently, a municipal solid waste landfill double liner system that was constructed in 1988 was exhumed. The HDPE geomembranes of this liner system had been exposed to varying degrees of leachate since 1989. Samples of the HDPE were extracted from the in-place liner system and were laboratory-tested for physical, mechanical and endurance properties. The selected suite of tests duplicated the test protocol conducted in 1988 as part of the liner system construction quality assurance (CQA) program.

The results of this testing show that the HDPE properties are still within the range of data generated by the original testing in 1988. No degradation in properties was indicated by this testing program. The HDPE had been exposed to the leachate, methane, and static and dynamic stresses for approximately 8 years. The results of this test program support the design selection of HDPE as the synthetic barrier component of this landfill liner system.     

Effect of leachate composition on the long-term performance of a HDPE geomembrane

Aging of the same geomembrane immersed in the same four synthetic municipal solid waste leachates tested by Rowe et al. (2008) for 2.65 years is continued for an additional 6.5 years (i.e., providing data over more than 9 years of aging). The additional data is used to (a) update the initial estimates for antioxidant depletion stage, and (b) investigate the effect of leachate constituents on the timing and magnitude of the changes in the physical properties of the geomembrane. While all the examined leachates had surfactant and trace metals in common, reduced Leachate 1 (full leachate) had salts and volatile fatty acids (VFAs), Leachate 2 was not reduced and had neither salts nor VFAs, reduced Leachate 3 had salts, reduced Leachate 4 had VFAs, and Leachate 5 was similar to Leachate 2 except that it was reduced. Incubation in all leachates gave very similar predictions of the antioxidant depletion stage, however, the salts in Leachates 1 and 3 are shown to have the largest effect on the geomembrane mechanical properties, especially stress-crack resistance, resulting in a shorter time to nominal failure than for leachates without salts. Furthermore, reduced Leachates 1 and 3 showed faster degradation in stress-crack resistance than Leachate 2 which was not reduced and without salts. Arrhenius modeling is used to extrapolate the time to nominal failure (i.e., a reduction in stress-crack resistance to 150 h) at a range of temperatures.     

Evaluating barrier performance of geomembranes against 1,4-dioxane and bisphenol a in landfill leachates

Previous studies have shown that within a month benzene easily passes through geomembranes (PVC, LDPE, and HDPE geomembranes). This study uses diffusive permeation tests to clarify the barrier performance of geomembranes against bisphenol A and 1,4-dioxane, which have been detected in some Japanese waste leachates. Although dissolved bisphenol A can be adsorbed on the geomembranes, it does not pass through them during the testing period (at least 400 days are required for it to completely pass through 0.5-mm-thick PVC geomembranes). In addition, dissolved 1,4-dioxane is not adsorbed on any geomembranes and hardly passes through any of them (at least five years are required for it to completely pass through 0.5-mm-thick PVC geomembranes). Thus, geomembranes exhibit a good barrier performance against these two organic compounds, especially 1,4-dioxane.     

Interface transmissivity of conventional and multicomponent GCLs for three permeants

A laboratory investigation of the interface transmissivity is reported for five different geosynthetic clay liners (GCLs) and a range of different geomembranes (GMBs) for a range of stresses from 10 to 150?kPa. The GCLs were prehydrated under normal stress before permeation. The GCLs examined comprised three multicomponent (a smooth coated, a smooth laminated, and textured coated) and two conventional (one with granular and one with powdered sodium bentonite) GCLs. The effect of a 4?mm circular defect in the coating of a multicomponent GCL directly below the 10?mm diameter hole in the GMB is investigated. The effect of GMB stiffness and texture is examined. Additionally, the effect of hydration and permeation of smooth coated GCL with highly saline solution and synthetic landfill leachate (SL3) is presented. It is shown that the 2-week interface transmissivity (θ_2-week) can be one to two orders of magnitude higher than steady-state interface transmissivity (θ _steady-state) at low stresses (10?kPa–50?kPa), whereas at high stresses (150?kPa) the variation is substantially less. For a smooth coated GCL hydrated and permeated with reverse osmosis (RO) water, GMB stiffness and texture has a limited effect on interface transmissivity when the coating is placed in contact with GMB at normal stresses of 10?kPa–150?kPa, whereas coating indentations result in much high interface transmissivity when placed in contact with GMB. GCL prehydration and permeation with highly saline solutions leads to higher interface transmissivity compared to RO water. With a 4.0?mm defect in the coating, the interface transmissivity between the coating and woven geotextile is higher than that between the coating and GMB for the stress levels and GCL examined.     

Degradation behaviour of HDPE geomembranes with high and low initial high-pressure oxidative induction time

The degradation of three high density polyethylene geomembranes (GMBs) (denoted xA, xB and xC) when immersed in simulated landfill leachate at 85 °C is examined. All three GMBs met the requirements of the generic industry specification GRI-GM13 with respect to their performance properties. The large high-pressure oxidative induction time (HP-OIT) (i.e., 790 min for xB and 960 min for xC) combined with the relatively high level of trace nitrogen detected, suggest the presence of hindered amine light stabilizers (HALS) as part of the antioxidant package in these GMBs, whereas, the relatively low initial HP-OITs (i.e., 260 min) and the low level of trace nitrogen for xA, suggest the absence of HALS in xA. Although xA had the lowest initial standard Std-OIT (Std-OIT was 115, 158 and 175 min for xA, xB and xC, respectively) it exhibited the longest time to antioxidant depletion based on Std-OIT. For the three GMBs, the HP-OIT depleted following exponential decay model until reaching a residual value. xB had the slowest HP-OIT depletion (0.016 month⁻¹) and was still depleting without reaching a residual value at the end of this study (after 46 months). xA experienced the fastest HP-OIT depletion (∼62 times faster than of xB) and reached a residual value of 78 min. For xC, HP-OIT depleted 40 times faster than for xB reaching a residual value (∼610 min) that was still higher than the HP-OIT of 400 min specified by GRI-GM13 for a new GMB. xB had the longest time to nominal failure despite having the lowest initial SCR value (330 h for xB compared to 910 and 800 h for xA and xC, respectively) and not having the highest OITs values. Although xC had a residual HP-OIT of 610 min, the SCR, melt index (MI) and tensile properties for xC had decreased to the point that xC was at nominal failure, indicating that the degradation can take place without the total depletion of antioxidants/stabilizers captured by the HP-OIT.     

Removal of leachate pollutants using flocculation method at simultaneous factors of optimum pH and Tacca leontopetaloides biopolymer flocculant (TBPF) dosage via face-centred central composite design

The effect of the interaction factor between pH and dosage is important in leachate wastewater treatment. This study aims to remove leachate pollutants such as turbidity, total suspended solid (TSS), chemical oxygen demand (COD) and colour using simultaneous factors of plant-based Tacca leontopetaloides biopolymer flocculant (TBPF) dosage and leachate pH. The flocculation process was carried out through jar test by applying the perikinetic theory and statical analysis (face-centred central composite design). The results found that the optimum leachate pH and TBPF dosage were pH 3 and 150 mg/L, respectively. The highest removal of leachate pollutants reached up to 69% with a second-order perikinetic model; R² = 0.9545 and k = 9 × 10⁻⁶ L/mg/min were obtained. Simultaneous interaction factors between leachate pH and TBPF dosage on turbidity and TSS removal were found significant and hence can be applied in the actual leachate wastewater treatment industry, particularly at the primary stage using the proposed model.