Risk control of heavy metal in waste incinerator ash by available solidification scenarios in cement production based on waste flow analysis

Incineration is a common method in municipal solid waste management, which has several advantages such as reducing the volume of waste, but with concerns about exhaust gas and ash management. In this study, heavy metals in bottom ash, secondary furnace ash and fly ash of two waste incinerators in Tehran and Nowshahr were analyzed and its control in cement production was investigated. For this purpose, twelve monthly samples of three types of incinerator ash were analyzed. By combining the studied ashes in the raw materials, the quantity of metals in the cement was analyzed. Finally, by investigating four scenarios based on quantitative variations in the routes of municipal solid waste, ash quantity and the related risk caused by its heavy metals were studied. The results showed that the concentration of heavy metals in the three ash samples of the studied incinerators was 19,513-23,972 µg/g and the composition of the metals included Hg (less than 0.01%), Pb (2.93%), Cd (0.59%), Cu (21.51%), Zn (58.7%), As (less than 0.01%), Cr (15.88%), and Ni (0.91%). The best quality of produced cement included 20% ash and 10% zeolite, which was the basis of the next calculations. It was estimated that the reduction of the release of metals into the environment includes 37 gr/day in best scenario equal to 10.6 tons/year. Ash solidification can be considered as a complementary solution in waste incinerator management.

Immobilization of polypyrrole on waste face masks using a novel in-situ-surface polymerization method: Removal of Cr(VI) from electroplating wastewater

AbstractIn this work, polypyrrole (PPy) was synthesized on the surface of waste surgical face masks (SFM) with a novel environmentally-friendly in-situ-surface polymerization approach and used as an adsorbent for removing hexavalent chromium (Cr(VI)). In this method, the SFM surface was activated using KMnO₄, resulting in the immobilization of porous MnO₂, on which pyrrole can be polymerized efficiently. The novelty of this method is the presence of the oxidant on the surface before the polymerization step, which results in a better surface modification with polypyrrole. This method provides adsorbents with higher adsorption capacity compared to the conventional polymerization method with ammonium persulfate (APS). The adsorbent prepared at the mass ratios of 1.0 and 2.0; respectively, for KMnO₄/SFM and pyrrole/SFM showed the highest performance. The adsorbent characterization revealed the successful polymerization of pyrrole on the surface of SFM. Reusability of the KMnO₄ and pyrrole solutions were successful with remarkable results, showing the advantage of this technique compared to the conventional polymerization method with APS. The effect of different factors on the adsorption process was investigated. The removal rate was around 98% under the optimum conditions (pH, 2; adsorbent dosage, 3 g L^-1; contact time, 60 min). The equilibrium data were well fitted by Langmuir isotherm (R²= 0.9999). Kinetic investigations revealed that the adsorption process fitted well with the pseudo-second-order model. The adsorbent was regenerated for up to five cycles. One of the most important advantages of the proposed method compared to other methods is the reduction of wastewater during the synthesis process.

Optimizing the effect of hydrochar on anaerobic digestion of organic fraction municipal solid waste for biogas and methane production

BACKGROUND

Anaerobic digestion (AD) is the biological waste treatment method for the organic fraction of municipal solid waste (OFMSW). AD is notable for its ability to reduce volume and produce biogas from waste. However, the conventional AD of OFMSW has a low degradation rate. In recent years, some treatment method has been used to promote the biogas and methane production of AD. One of these methods is hydrothermal carbonization (HTC).

PURPOSE

This study aimed to evaluate the effect of hydrothermal carbonization (HTC) temperature and hydrochar: OFMSW ratio as factors on biogas production, methane production, and methane content of anaerobic digestion (AD) as responses was investigated.

METHODS

This study determined the biomethane potential of raw and pretreated OFMSW (hydrochars) in 118 ml serum glass bottles. Based on the Hansen method, all tests were conducted at mesophilic temperature (37 ± 1 °C) in an incubator for 45 days. The response surface method and central composite model were used for designing experimental conditions. Quadratic models were used to estimate the correlation between factors and responses. Also, the optimal conditions for maximizing responses were determined.

RESULTS

Biogas production of mixing hydrochar and OFMSW was 41% more than control groups which contained OFMSW and inoculum. The optimal operating conditions to maximize all responses were applied in HTC temperature and hydrochar: OFMSW ratio of 179.366 °C and 2.406, respectively. In this condition, the maximum biogas production, methane production, and methane content were 394 mL/g VS, 284.351 mL/g VS, and 73.176%, respectively.

CONCLUSION

As an OFMSW HTC pretreatment for AD, hydrochar additive has a significantly positive and negative effect on biogas production, methane production, and methane content of biogas depending on operating conditions. Therefore. It is necessary to consider the individual and interaction effects of the temperature and hydrochar: OFMSW ratio, obtain the optimal conditions and determine responses.

Determining the appropriate mixing ratio in a multi-substrate anaerobic digestion of organic solid wastes employing Taguchi method

The current research proposed a method for optimally combining feed input ratios in order to improve the quantity and quality of daily biogas production through optimizing the variable response level in the Taguchi method. The anaerobic digestion (AD) process of an existing plant in Iran was simulated through a set of two-stage pilot reactors under mesophilic temperature conditions in order to achieve optimal operational performance. Three common substrates (organic fraction of municipal solid wastes, fruit and vegetable wastes, and horse manure) along with two recirculated materials; the post-digestion sludge and the secondary digester slurry, were investigated in 16 experimental runs based on four different pre-surface hypotheses. Comparison of the results of daily biogas energy (J/d/g-VS) in Run#9, to which the actual yield of hydrogen sulfide was minimal in parallel to a methane yield above 100 mL/g-VS, with the result of the optimal run with the ratios provided by the model, showed that the daily biogas energy was improved by 50% comparing to the control Run that had similar conditions to which was being applied in the full-scale existing AD plant.

The effects of co-substrate and thermal pretreatment on anaerobic digestion performance

The influence of anaerobic co-digestion of leachate and sludge with organic fraction of municipal solid waste (OFMSW) under mesophilic condition in three batch digesters of 5 L capacity has been studied. OFMSW was mixed with leachate and sludge at three different ratios. Experimental results illustrated that the digester with a ratio of 2000/2500 (leachate (mL) or sludge/OFMSW (mL)) had significantly higher performance. Furthermore, this study compared the performance of anaerobic digestion of different substrates with three different mixing ratios with and without thermal pretreatment at low temperature (65°C) in terms of biogas production, chemical oxygen demand (COD) elimination as well as hydraulic retention time. In addition, to predict the biogas yield and evaluate the kinetic parameters, the modified Gompertz model was applied. Based on the results, the maximum biogas yield from adding different leachate and sludge ratios to OFMSW was recorded to be 0.45 and 0.38 m³kg^-1 COD which was higher about 7% in comparison with co-digestion original OFMSW without thermal pretreatment. In addition, thermal pretreatment accelerated the hydrolysis step. Moreover, the total COD elimination was relatively stable in the range of 52-60% at all types of substrate mixtures. Also, the modified Gompertz model demonstrated a good fit to the experimental results.

ABBREVIATIONS

AD: anaerobic digester; BOD: biochemical oxygen demand; COD: chemical oxygen demand; FAAS: flame atomic absorption spectroscopy; HS: high solids; HRT: hydraulic retention time; LS: low solids; MS: medium solids; OFMSW: organic fraction of municipal solid waste; TCD: thermal conductivity detector; TS: total solid; TSS: total suspended solids.

Stimulation of the hydrolytic stage for biogas production from cattle manure in an electrochemical bioreactor

Electrical current in the hydrolytic phase of the biogas process might affect biogas yield. In this study, four 1,150 mL single membrane-less chamber electrochemical bioreactors, containing two parallel titanium plates were connected to the electrical source with voltages of 0, -0.5, -1 and -1.5 V, respectively. Reactor 1 with 0 V was considered as a control reactor. The trend of biogas production was precisely checked against pH, oxidation reduction potential and electrical power at a temperature of 37 ± 0.5°C amid cattle manure as substrate for 120 days. Biogas production increased by voltage applied to Reactors 2 and 3 when compared with the control reactor. In addition, the electricity in Reactors 2 and 3 caused more biogas production than Reactor 4. Acetogenic phase occurred more quickly in Reactor 3 than in the other reactors. The obtained results from Reactor 4 were indicative of acidogenic domination and its continuous behavior under electrical stimulation. The results of the present investigation clearly revealed that phasic electrical current could enhance the efficiency of biogas production.

Attenuation of municipal landfill leachate through land treatment

The treatment of municipal landfill's leachate is considered as one of the most significant environmental issues. In this study a laboratory experiment was conducted through land treatment, achieving an efficient and economical method by using Vetiver plant. Moreover, the effects of land treatment of leachate of municipal landfills on the natural reduction of organic and inorganic contaminants in the leachate after the pre-treatment in the Aradkouh disposal center are invested. Three pilots including the under-investigation region's soil planted by Vetiver plant, the region's intact soil pilot and the artificial composition of the region's soil including the natural region's soil, sand, and rock stone are used. The leachate, having passed its initial treatment, passed through the soil and to the pilot. It was collected in the end of the pilots and its organic and inorganic contaminants were measured. However, the land treatment of leachate was conducted in a slow rate at various speeds. According to the results, in order to remove COD, BOD5, TDS, TSS, TOC the best result was obtained in the region's soil planted with Vetiver plant and at the speed of 0.2 ml per minute which resulted 99.1%, 99.7%, 52.4%, 98.8%, 94.9% removal efficiencies, respectively. It also can be concluded that the higher the organic rate load is, the lower the efficiency of the removal would be. In addition, EC & pH were measured and the best result was obtained in the region's soil planted with Vetiver plant and at the speed of 0.2 ml/min.

A performance-based method for calculating the design thickness of compacted clay liners exposed to high strength leachate under simulated landfill conditions

Compacted clay liners (CCLs) when feasible, are preferred to composite geosynthetic liners. The thickness of CCLs is typically prescribed by each country's environmental protection regulations. However, considering the fact that construction of CCLs represents a significant portion of overall landfill construction costs; a performance based design of liner thickness would be preferable to 'one size fits all' prescriptive standards. In this study researchers analyzed the hydraulic behaviour of a compacted clayey soil in three laboratory pilot scale columns exposed to high strength leachate under simulated landfill conditions. The temperature of the simulated CCL at the surface was maintained at 40 ± 2 °C and a vertical pressure of 250 kPa was applied to the soil through a gravel layer on top of the 50 cm thick CCL where high strength fresh leachate was circulated at heads of 15 and 30 cm simulating the flow over the CCL. Inverse modelling using HYDRUS-1D indicated that the hydraulic conductivity after 180 days was decreased about three orders of magnitude in comparison with the values measured prior to the experiment. A number of scenarios of different leachate heads and persistence time were considered and saturation depth of the CCL was predicted through modelling. Under a typical leachate head of 30 cm, the saturation depth was predicted to be less than 60 cm for a persistence time of 3 years. This approach can be generalized to estimate an effective thickness of a CCL instead of using prescribed values, which may be conservatively overdesigned and thus unduly costly.

Characterization of oily sludge from a Tehran oil refinery

In this study, oily sludge samples generated from a Tehran oil refinery (Pond I) were evaluated for their contamination levels and to propose an adequate remediation technique for the wastes. A simple, random, sampling method was used to collect the samples. The samples were analyzed to measure Total petroleum hydrocarbon (TPH), polyaromatic hydrocarbon (PAH) and heavy metal concentrations in the sludge. Statistical analysis showed that seven samples were adequate to assess the sludge with respect to TPH analyses. The mean concentration of TPHs in the samples was 265,600 mg kg⁻¹. A composite sample prepared from a mix of the seven samples was used to determine the sludge's additional characteristics. Composite sample analysis showed that there were no detectable amounts of PAHs in the sludge. In addition, mean concentrations of the selected heavy metals Ni, Pb, Cd and Zn were 2700, 850, 100, 6100 mg kg⁻¹, respectively. To assess the sludge contamination level, the results from the analysis above were compared with soil clean-up levels. Due to a lack of national standards for soil clean-up levels in Iran, sludge pollutant concentrations were compared with standards set in developed countries. According to these standards, the sludge was highly polluted with petroleum hydrocarbons. The results indicated that incineration, biological treatment and solidification/stabilization treatments would be the most appropriate methods for treatment of the sludges. In the case of solidification/stabilization, due to the high organic content of the sludge, it is recommended to use organophilic clays prior to treatment of the wastes.