Mohammad Zain Khan

Waste biorefineries : Enabling circular economies in developing countries

This paper aims to examine the potential of waste biorefineries in developing countries as a solution to current waste disposal problems and as facilities to produce fuels, power, heat, and value-added products. The waste in developing countries represents a significant source of biomass, recycled materials, chemicals, energy, and revenue if wisely managed and used as a potential feedstock in various biorefinery technologies such as fermentation, anaerobic digestion (AD), pyrolysis, incineration, and gasification. However, the selection or integration of biorefinery technologies in any developing country should be based on its waste characterization. Waste biorefineries if developed in developing countries could provide energy generation, land savings, new businesses and consequent job creation, savings of landfills costs, GHG emissions reduction, and savings of natural resources of land, soil, and groundwater. The challenges in route to successful implementation of biorefinery concept in the developing countries are also presented using life cycle assessment (LCA) studies.

Bioremediation of 2-chlorophenol containing wastewater by aerobic granules-kinetics and toxicity.

2-Chlorophenol (2-CP) degrading aerobic granules were cultivated in a sequencing batch reactor (SBR) in presence of glucose. The organic loading rate (OLR) was increased from 6.9 to 9.7 kg COD m(-3)d(-1) (1150-1617 mg L(-1)COD per cycle) during the experiment. The alkalinity (1000 mg L(-1) as CaCO(3)) was maintained throughout the experiment. The specific cell growth rate was found to be 0.013 d(-1). A COD removal efficiency of 94% was achieved after steady state at 8h HRT (hydraulic retention time). FTIR, UV, GC, GC/MS studies confirmed that the biodegradation of 2-CP occurs via chlorocatechol (modified ortho-cleavage) pathway. Biodegradation kinetics followed the Haldane model with kinetic parameters: V(max)=840 mg2-CPgMLVSS(-1)d(-1), K(s)=24.61 mg L(-1), K(i)=315.02 mg L(-1). Abiotic losses of 2-CP due to volatilization and photo degradation by sunlight were less than 3% and the results of genotoxicity showed that the degradation products are eco-friendly.

Degradation pathway, toxicity and kinetics of 2,4,6-trichlorophenol with different co-substrate by aerobic granules in SBR.

The present study deals with cultivation of 2,4,6-trichlorophenol (TCP) degrading aerobic granules in two SBR systems based on glucose and acetate as co-substrate. Biodegradation of TCP containing wastewater starting from 10 to 360 mg L(-1) with more than 90% efficiency was achieved. Sludge volume index decreases as the operation proceeds to stabilize at 35 and 30 mL g(-1) while MLVSS increases from 4 to 6.5 and 6.2 g L(-1) for R1 (with glucose as co-substrate) and R2 (with sodium acetate as co-substrate), respectively. FTIR, GC and GC/MS spectral studies shows that the biodegradation occurred via chlorocatechol pathway and the cleavage may be at ortho-position. Haldane model for inhibitory substrate was applied to the system and it was observed that glucose fed granules have a high specific degradation rate and efficiency than acetate fed granules. Genotoxicity studies shows that effluent coming from SBRs was non-toxic.

Bioelectricity Generation and Bioremediation of an Azo-Dye in a Microbial Fuel Cell Coupled Activated Sludge Process

Simultaneous bioelectricity generation and dye degradation was achieved in the present study by using a combined anaerobic-aerobic process. The anaerobic system was a typical single chambered microbial fuel cell (SMFC) which utilizes acid navy blue r (ANB) dye along with glucose as growth substrate to generate electricity. Four different concentrations of ANB (50, 100, 200 and 400 ppm) were tested in the SMFC and the degradation products were further treated in an activated sludge post treatment process. The dye decolorization followed pseudo first order kinetics while the negative values of the thermodynamic parameter ∆G (change in Gibbs free energy) shows that the reaction proceeds with a net decrease in the free energy of the system. The coulombic efficiency (CE) and power density (PD) attained peak values at 10.36% and 2,236 mW/m2 respectively for 200 ppm of ANB. A further increase in ANB concentrations results in lowering of cell potential (and PD) values owing to microbial inhibition at higher concentrations of toxic substrates. Cyclic voltammetry studies revealed a perfect redox reaction was taking place in the SMFC. The pH, temperature and conductivity remain 7.5–8.0, 27(±2°C and 10.6–18.2 mS/cm throughout the operation. The biodegradation pathway was studied by the gas chromatography coupled with mass spectroscopy technique, suggested the preferential cleavage of the azo bond as the initial step resulting in to aromatic amines. Thus, a combined anaerobic-aerobic process using SMFC coupled with activated sludge process can be a viable option for effective degradation of complex dye substrates along with energy (bioelectricity) recovery.

Feasibility study on anaerobic biodegradation of azo dye reactive orange 16

Anaerobic digestion of textile azo-dyes is very effective and widely used since it is cost-effective and energy efficient. The present study deals with the anaerobic degradation of reactive orange 16 (RO 16, an azo-dye) using mixed microbial culture. 80 mL each of three different concentrations of RO 16 (100, 200 and 300 ppm) were taken in 150 mL serum vials containing 20 mL of mixed microbial culture and studied periodically. HPLC and UV data revealed that more than 90% of the color was removed within the very first week of the reactor startup. A high COD removal efficiency (≥80%) was achieved after the steady state. Methane and VFAs were produced, and monitored by Gas chromatography. The pH of the medium was slightly acidic favoring methanogenic activity. The diversity of the microbial community was studied by denaturing gradient gel electrophoresis (DGGE) of the polymerase chain reaction (PCR) amplified products of the bacterial and archeal 16S rRNA and the results showed the presence of significant population of acetogens as well as methanogens in the reactor. Quantitative real time PCR (qPCR) was used for the quantitative analysis of some major genera. This study showed that strategic operation of the anaerobic digester can be a viable option for effective decolorization of a complex substrate resulting in energy (biogas) generation.

Bio-electro degradation of azo-dye in a combined anaerobic–aerobic process along with energy recovery

A combined anaerobic–aerobic process involving a single chambered microbial fuel cell (SMFC) followed by an aerobic downstream treatment process is selected for the complete removal of reactive orange 16 (RO 16) from contaminated water. The degradation of azo-dye in SMFC results in the formation of aromatic amines with simultaneous production of electricity. The degradation products of the SMFC were further treated in an activated sludge downstream process in order to provide complete solution from dye wastewater. More than 90% of the chemical oxygen demand (COD) was removed in the combined process for all the test concentrations. The maximum output cell potential and the coulombic efficiency (CE) were 423 mV and 3.4% respectively. SEM images of the mixed microbial culture showed the presence of cocci, diatoms and rod shaped bacteria. Cyclic voltammetry revealed that a perfect redox process took place in the SMFC system. The results of the gas chromatography coupled with the mass spectroscopy (GC/MS) technique showed that RO 16 was first converted into aromatic amines in SMFC which were further transformed into phthalic acid and finally into benzoic acid. The results of the present work demonstrate that wastewater containing complex and toxic dyes can be successfully treated in SMFC followed by aerobic post-treatment along with energy recovery.

Biodiesel production potential from fat fraction of municipal waste in Makkah

In the Kingdom of Saudi Arabia (KSA), millions of Muslims come to perform Pilgrimage every year. Around one million ton of municipal solid waste (MSW) is generated in Makkah city annually. The collected MSW is disposed of in the landfills without any treatment or energy recovery. As a result, greenhouse gas (GHG) emissions and contamination of the soil and water bodies along with leachate and odors are occurring in waste disposal vicinities. The composition of MSW shows that food waste is the largest waste stream (up to 51%) of the total generated MSW. About 13% of the food waste consists of fat content that is equivalent to about 64 thousand tons per year. This study aims to estimate the production potential of biodiesel first time in Makkah city from fat/oil fractions of MSW and highlight its economic and environmental benefits. It has been estimated that 62.53, 117.15 and 6.38 thousand tons of biodiesel, meat and bone meal (MBM) and glycerol respectively could be produced in 2014. A total electricity potential of 852 Gigawatt hour (GWh) from all three sources based on their energy contents, Higher Heating Value (HHV) of 40.17, 18.33 and 19 MJ/kg, was estimated for 2014 that will increase up to 1777 GWh in 2050. The cumulative net savings from landfill waste diversion (256 to 533 million Saudi Riyal (SAR)), carbon credits (46 to 96 million SAR), fuel savings (146 to 303 million SAR) and electricity generation (273 to 569 million SAR) have a potential to add a total net revenue of 611 to 1274 million SAR every year to the Saudi economy, from 2014 to 2050 respectively. However, further studies including real-time data about annual slaughtering activities and the amount of waste generation and its management are critical to decide optimum waste management practices based on life cycle assessment (LCA) and life cycle costing (LCC) methodologies.

Waste-to-Hydrogen Energy in Saudi Arabia: Challenges and Perspectives

Hydrogen (H2) has emerged as a promising alternative fuel that can be produced from renewable resources including organic waste through biological processes. In the Kingdom of Saudi Arabia (KSA), the annual generation rate of municipal solid waste (MSW) is around 15 million tons that average around 1.4 kg per capita per day. Similalry, a significant amount of industrial and agricultural waste is generated every year in KSA. Most of these wastes are disposed in landfills or dumpsites after partial segregation and recycling and without material or energy recovery. This causes environmental pollution and release of greenhouse gas (GHG) emissions along with public health problems. Therefore, the scope of producing renewable H2 energy from domestic and industrial waste sources is promising in KSA, as no waste-to-energy (WTE) facility exists. This chapter reviews the biological and chemical ways of H2 production from waste sources and availability of waste resources in KSA.

Efficient visible light photocatalytic activity and enhanced stability of BiOBr/Cd(OH)2 heterostructures

Novel BiOBr/Cd(OH)2 heterostructures were synthesized by a facile chemical bath method under ambient conditions. A series of BiOBr/Cd(OH)2 heterostructures were obtained by tuning the Bi/Cd molar ratios. The obtained heterostructures were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Optical properties were studied by UV-visible spectroscopy, diffuse reflectance spectroscopy and photoluminescence (PL). Photocatalytic studies on rhodamine B (RhB) under visible light irradiation showed that the heterostructures are very efficient photocatalysts in mild basic medium. Scavenger test studies confirmed that the photogenerated holes and superoxide radicals (O2˙−) are the main active species responsible for RhB degradation. Comparison of photoluminescence (PL) intensity suggested that an inhibited charge recombination is crucial for the degradation process over these photocatalysts. Moreover, relative positioning of the valence and conduction band edges of the semiconductors, O2/O2˙− and ˙OH/H2O redox potentials and HOMO–LUMO levels of RhB appear to be responsible for the hole-specificity of degradation. Photocatalytic recycling experiments indicated the high stability of the catalysts in the reaction medium without any significant loss of activity. This study hence concludes that the heterojunction constructed between Cd(OH)2 and BiOBr interfaces play a crucial role in influencing the charge carrier dynamics and subsequent photocatalytic activity.

Studies on the biodegradation of two different azo dyes in bioelectrochemical systems

A comparative study on the degradation of acid navy blue R (ANB) and reactive orange 16 (RO 16) was performed in two identical microbial fuel cells (MFCs) under similar conditions and the microbial communities were quantified using a quantitative real time polymerase chain reaction (qPCR). Electricity and methane gas were produced as the end products along with the significant removal of chemical oxygen demand (COD) during the study. The overall performance in terms of degradation rate, COD removal efficiency and biogas production rates were slightly better in the case of the reactor using RO 16 as the carbon source, while electricity production was slightly greater in the reactor treating ANB. A negative standard reduction potential of the reaction mixture indicates the presence of oxidized species in the reactor. Scanning electron microscopy images show the presence of diatoms and rod shaped bacteria in the mixed microbial culture and also confirmed the formation of a biofilm on the anode surface. The qPCR technique was used as a quantitative tool to estimate the abundance of methanogens, sulphate reducing bacteria (SRBs) and electrochemically active Geobacter species. The relative abundance of methanogens was comparatively higher and Geobacter was lower in the case of the reactor treating RO 16. Although the output power was low, this technique can be used for the effective degradation of complex and toxic compounds.