Washing of wheat straw to improve its combustion properties with energy recovery by anaerobic digestion of the washwater

Wheat straw is a major potential source of waste biomass for renewable energy production, but its high salt content causes problems in combustion. Work was undertaken to evaluate straw washing as a means of reducing the alkali index of the straw by washing out light metal cations, primarily potassium. In addition to loss of salts, organic matter is also washed out of the straw and this is a potential source of energy through anaerobic biodegradation to produce methane as a fuel gas. The rate of washout of both potassium and organic carbon was dependent on the temperature of the washwater, although cold water washing could reduce the alkali index to a suitable level, after a long retention time. Using this technique an organically dilute washwater was produced with a chemical oxygen demand of around 2.0 g l-1, suitable for a short hydraulic retention time immobilised cell digester. An upflow anaerobic sludge blanket (UASB) was chosen for initial trials, but this was later compared with an anaerobic filter. As a control throughout the experiments digesters were also maintained on a synthetic wastewater which gave a performance baseline against which the activity and methane production potential of the UASB digesters could be judged. Initial trials showed an accumulation of potassium in the granular sludge bed and an initial apparent drop in the specific methane production and COD removal efficiency. This could be recovered and the potassium washed out of the bed by switching the feed from wheat straw washwater (WSW) to synthetic sewage. Repetitive cycling between these two substrates did not damage or disrupt the digestion process. When allowed to stabilise on WSW alone the COD removal was around 83% and the specific methane production was 0.216 l g-1 CODadded under pseudo steady state conditions. The accumulation of potassium also stabilised at around 11 mg g-1 granule wet weight. Under these conditions the organic loading rate could be increased to ~3 g COD l-1 day-1 without adversely affecting digester performance. Whilst operating on wheat straw washwater the conversion of COD to methane compared to the stoichiometric potential was less than that seen for the synthetic wastewater in the same digester with the same granular biomass. It is hypothesised that a proportion of the carbon converted is used in maintaining the osmotic integrity of the cells by a metabolically-linked potassium transport system. Evidence to show intracellular accumulation of potassium was provided by transmission electron microscopy coupled to EDX analysis of granular sections. Complementary studies were carried out to determine the resistance to salt toxicity of two different types of anaerobic inoculum, taken from a mesophilic municipal wastewater biosolids digester and a saline estuarine mud, for comparison with the UASB granules. Both of these inoculums had a higher tolerance to both Na and K than the granular material, and the wastewater plant digestate was used to further acclimate a dispersed growth inoculum to seed an anaerobic filter. In the acclimatisation, which was carried out in semi-continuous fed stirred tank digesters, the digestate successfully acclimated to 10 g l-1 of KCl, NaCl and a mixture of the two salts. When operated at the same loading on either synthetic wastewater or WSW there was no difference between performance of the UASB and anaerobic filter in either COD removal efficiency or specific methane production.A simple energy balance was conducted taking into account only the energy required for heating washwater to reduce the washing time necessary to meet the alkali index for the straw. This would, however, consume most of the energy produced by anaerobic digestion of the washwater even when other energy consuming activities were not considered

Anaerobic digestion of domestic wastewater in different salinity levels: the adaptation process

The effect of osmotic stress was carried out to determine the resistance to salt toxicity using 4 Continuous Stirred Tank Reactor (CSTR). A CSTR digestion study revealed that digesters seeded with an inoculum from a conventional mesophilic digester treating municipal wastewater and fed on domestic wastewater (DW) plus salts were able to acclimate successfully to a final salt concentration of 10 g l-1. The digesters showed some disturbances during the acclimatisation period as indicated by reductions in specific methane production (SMP), specific biogas production (SBP), pH and increases in Intermediate Alkalinity /Partial Alkalinity (1A/PA) ratio and Volatile Fatty Acid (VFA) concentration. This study revealed the order of disturbance was Sodium Chloride (NaCl) > Potassium Chloride (KCl) > KCl + NaCl. The average values for SMP after stabilisation were below those in the controlled digester, at 0.335 (controlled), 0.323 (NaCl), 0.316 (KCl + NaCl) and 0.308 l CH4 g-1 COD added (KCl)

Preliminary assessment of lakes water quality status at campus area in Selangor, Malaysia

A study was conducted to assess the water quality status of Engineering and Serumpun Lakes located in campus area. Selected water quality parameters (Biochemical Oxygen Demand - BOD, Chemical Oxygen Demand - COD, Dissolved Oxygen - DO, turbidity, Suspended Solids - SS, pH and Ammonia Nitrogen-NH3-N) were determined for about two months observation in the wet season and the average results were compared to Malaysian standards. The status of lakes were determined by using Water Quality Index (WQI) and classified according to the Interim National Water Quality Standards (INWQS), Malaysia. The observed values for seven parameters of Engineering Lake were classified as IIA/B and V classes as well as Serumpun Lake. From the results, the lakes can be used for recreational purposes. However, based on WQI calculated value, the status of the lakes during the study period was indicated as polluted; 31.6 and 32.5 for Engineering and Serumpun lakes, respectively. Both lakes were classified as Class IV and the water suitable for irrigation uses only

Manufacture of Low-cost Activated Carbon using Sago Palm Bark and Date Pits by Physicochemical Activation

Two raw materials, sago palm bark (SPB) and date pits, were utilized as precursors to prepare high porosity activated carbon (AC). The porosity of these two raw materials was compared with that of commercial AC made from coconut shells. The physicochemical activation method was used for AC preparation, and it consisted of two steps, carbonization and activation. The activation process was performed using zinc chloride (ZnCl2) as an activation agent. N2 adsorption-desorption analysis was carried out to characterize the porosity of AC. Thermogravimetric analysis (TGA) was conducted for the two raw materials. The adsorbent made from SPB, which showed the maximum surface area of 1634 m2/g at the 700 °C activation temperature for one hour, while the surface area of prepared AC from date pits was 1367 m2/g. Both prepared ACs had a larger surface area than commercial AC made with coconut shell (1348 m2/g)

Co-digestion of rice straw leachate and domestic wastewater for biogas production with addition of urea as nitrogen source

This study investigates the methane production by anaerobic co-digestion of rice straw leachate (RSL) and domestic wastewater (WW). The experiment was conducted at a controlled mesophilic temperature of 38°C in Continuous Glass Reactor (CGR) for a period of approximately 12 weeks. The process performance was evaluated based on the efficiency of COD removal and methane production in relation to other parameters such as pH, (organic loading rate) OLR and alkalinity. This study confirmed that the rate of COD removal for co-digestion of WW and RSL achieved the stable condition at 89.33%, meanwhile the digestion of RSL with addition of urea was at 76.00%. The addition of urea into RSL, showed the synergistic effect in anaerobic digestion as the removal rate of COD increased from 61.33% to 76.00%. Meanwhile, methane production reached the highest value of 0.154 L/CH4 at day 32 with the COD conversion ratio of 81.33%. SEM analysis showed a change in surface structure of the granules and it was confirmed by EDX analysis that there was some light metal crystallisation and salt agglomeration on the sludge granule surface

Atmospheric Iron and Aluminium Deposition and Sea-Surface Dissolved Iron and Aluminium Concentrations in the South China Sea off Malaysia Borneo (Sarawak Waters)

South China Sea (SCS) is an oligotrophic sea which usually receives low nutrients supply. However, massive atmospheric dust input was occurred during the haze event in Southeast Asia for almost every year. The input of dissolved iron (DFe) and dissolved aluminium (DAl) from dust and nearby land into SCS off Sarawak Borneo region during the worst haze event in 2015 of the Southeast Asia were investigated. The estimation dust deposition during this study was 0.162 mg/m2/yr. The atmospheric fluxes of total Fe and total Al at the offshore Sarawak waters were 0.611 µmol/m2/yr and 2.03 µmol/m2/yr, respectively, where the readily available dissolved Fe and Al from the dust were 0.11 µmol/m2/yr (DFe) and 0.31 µmol/m2/yr (DAl). Fe has higher solubility (17.78%) than Al (15.21%). The lateral fluxes (e.g. from the nearby land) were 37.08 nmol/m2/yr (DFe) and 125 nmol/m2/yr (DAl), with strong Fe organic ligand class L1 (log K:22.43 – 24.33). High concentrations of DFe and DAl at the surface water of the offshore region, coincided with high concentration of macronutrients due to the prevailing south-westerly winds originated from the west Kalimantan. Low residence times, ~0.92 (DFe) and ~1.31 (DAl) years, corresponded well with DAlexcess in surface seawater due to biological utilization of DFe. Future works emphasize on natural organic Fe(III) ligands and phytoplankton study are needed for better understanding on biogeochemistry of Fe and Al at SCS off Malaysia Borneo

Heat transfer coefficients and yield analysis of a double-slope solar still hybrid with rubber scrapers: an experimental and theoretical study

In this study, a new double-slope solar still hybrid with rubber scrapers (DSSSHS) and a double-slope solar still (DSSS) were designed, manufactured and tested. The proposed design of DSSSHS makes use of the advantages of using a small slope of the condensing cover of the still that allows higher solar radiation to enter into the still. Disadvantages resulting from using the small slope are overcome by using the rubber scrapers. No researcher has yet used the scrapers in solar still. Experimental measurements and results were used to calculate the theoretical values of convective and evaporative heat transfer coefficients, in addition to the theoretical values of the yields. Results of the two models were compared to evaluate the advantages of using rubber scrapers in the new model. Using rubber scrapers in DSSSHS model enhanced the total internal heat transfer coefficient (h1) as well as the productivity. The maximum recorded value of the total internal heat transfer coefficient for the DSSSHS is found as 38.754 W/m2 °C and the daily yield as 4.24 L/m2 day with productivity improvement of 63%, for the case when the inclination angle of the glass cover is quite small (about 3.0°)

Treatment of wastewater from a food and beverage industry using conventional wastewater treatment integrated with membrane bioreactor system : a pilot scale case study

This study compares the performance of the Hollow Fiber (HF) and Flat Sheet (FS) types of membrane bioreactors (MBRs) for the treatment of food and beverage (F&B) industry wastewater in a pilot-scale study of a wastewater treatment plant (WWTP). HF and FS membrane configurations were evaluated at two different Mixed Liquor Suspended Solid (MLSS) levels: 6000 mg/L and 12,000 mg/L. The performance of each configuration was evaluated in terms of Chemical Oxygen Demand (COD) and Total Suspended Solid (TSS) removals for effluent quality measurement. The transmembrane pressure (TMP), flux rate, and silt density index (SDI) were monitored and calculated for membrane fouling assessment. The results show that the rejection rates of COD and TSS for HF and FS membrane types were more than 84% for the two different MLSS levels. During the study, the HF membrane recorded 0.3 bar transmembrane pressure, which complies with the recommended range (i.e., two to three times of chemical cleaning). On the other hand, the FS membrane operates without chemical cleaning, and the TMP value was below the recommended range at 0.2 bar. It was found that the flux values recorded for both the HF and FS systems were within the recommended range of 40 L/m2/h. Analysis of SDI revealed that the calculated index ranged between 1 and 2.38 and was within the allowable limit of 3. Both types of MBR consistently achieved an 80% to 95% rejection rate of COD and TSS. Effluent quality measurement of treated F&B wastewater in this pilot-scale study using a WWTP integrated with an MBR indicated a good achievement with compliance with the Malaysia industrial effluent discharge standards

Concentrations of Cadmium, Copper, and Zinc in Macrobrachium rosenbergii (Giant Freshwater Prawn) from Natural Environment

This study analyzed the levels of cadmium (Cd), copper (Cu), and zinc (Zn) by the flame atomic absorption spectrophotometer (FAAS), in the muscle tissues, exoskeletons, and gills from freshwater prawn (Macrobrachium rosenbergii) (n = 20) harvested from natural habitat in Kerang River, Malaysia on 25th November 2015. Significant increase of the metals level in muscle tissue and gill (r > 0.70, p < 0.05) were observed with increase in length except for Cu in gills. No relationship was found between metals level in exoskeleton and length. The concentrations of Cd, Cu and Zn were significantly higher (p < 0.05) in males (muscle tissues and exoskeleton) except for Cd in exoskeleton. In gills, only Cu was significantly higher (p < 0.05) in female than male. All samples contained metals below the permissible limit for human consumption (i.e., Cd < 2.00 mg/kg; Cu < 30.00 mg/kg; Zn < 150 mg/kg). Annual metals monitoring in prawn and environmental samples is recommended to evaluate changes of metals bioaccumulation and cycling in the system, which is useful for resources management. © 2018 Springer Science+Business Media, LLC, part of Springer Natur

Effects of electric potential, NaCl, pH and distance between electrodes on efficiency of electrolysis in landfill leachate treatment

This study investigated the effects of different parameters on the removal efficiencies of organic and inorganic pollutants in landfill leachate treatment by electrolysis. Different parameters were considered such as the electric potential (e.g., 24, 40 and 60 V), hydraulic retention time (HRT) (e.g., 40, 60, 80, 100 and 120 min), sodium chloride (NaCl) concentration (e.g., 1, 3, 5 and 7%), pH (e.g., 3, 7 and 9), electrodes materials [e.g., aluminum (Al) and iron (Fe)] and distance between electrodes (e.g., 1, 2 and 3 cm). The best operational condition of electrolysis was then recommended. The electric potential of 60 V with HRT of 120 min at 5% of NaCl solution using Al as anode and Fe as cathode (kept at a distance of 3 cm) was the most efficient condition which increased the removal efficiencies of various parameters such as turbidity, salinity, total suspended solids (TSS), total dissolved solids (TDS), biochemical oxygen demand (BOD), chemical oxygen demand (COD) and heavy metals (e.g., Zn and Mn). The higher removal percentages of many parameters, especially COD (94%) and Mn (93%) indicated that the electrolysis is an efficient technique for multi-pollutants (e.g., organic, inorganic and heavy metals) removal from the landfill leachate