Waleed M. Zahid

Suspended solids in biological filter effluents

Abstract Some physical properties of suspended solids in two trickling filter effluents were measured. Several size indices and shape factors of these particles were determined with the use of an image analysis system. The applicability of the sample preservation technique limited the studied particles to those with the longest dimension greater than 10 μm. The majority of the particles studied had diameters of less than 100 μm. The settling velocities and the sizes of the particles studied were measured in a quiescent water column by a multiexposure photographic technique. Results showed that particle settling velocity increased as a fractional power of size. Based on these direct measurements, the particle density was calculated, and found to decrease with an increase of the particle size.

Use of cloth-media filter for membrane bioreactor treating municipal wastewater

This study evaluated three different textile materials (Acrylate, Polyester, and Nylon) as filter media for MBR treating municipal wastewater. Chemical oxygen demand (COD) loading rates were 1.71, 1.65 and 1.84 g/l d while feed/microorganisms (F/M) ratios were 0.32, 0.31 and 0.33 in Reactor 1, Reactor 2 and Reactor 3, respectively. The actual hydraulic retention times were 8.6, 8.9 and 8.0 h in R1, R2 and R3. At 5.3-5.5 g/l mixed liquor suspended (MLSS) and 26.3 days solid retention time (SRT) the membrane bioreactors were effective in removing 93-95% of COD, 99% of total suspended solids (TSS) and turbidity, 89-94% of total kjeldahl nitrogen (TKN) and 90-96% of total ammonia nitrogen. Phosphorous removal was limited to 51-55% while faecal coliform was reduced by four logs. Quality of the treated effluents met both Saudi and Egyptian reuse standards for restricted irrigation and could be easily disinfected to meet the unrestricted irrigation standards.

A technique for a characterization of RBC biofilm surface

Abstract A new technique was developed to evaluate geometric irregularities of biofilm surface. Vertical microtome sections of RBC biofilm samples embedded in glycol methacrylate resin were cut in two perpendicular directions and their profiles were examined by light microscopy image analysis. The measured fractal dimensions of the studied RBC biofilm surface were in the broad range from 2.1 to 2.8. The hydrodynamic and mass transfer models for biofilm systems may be greatly improved by inclusion of numerical values characterizing the surfaces involved.

Physical stabilization and embedding of microbial aggregates for light microscopy studies

Abstract An improved technique for the physical stabilization of microbial aggregates, by embedding them in solidified agar, is recommended for light microscopy studies such as the measurement of size and the evaluation of morphological parameters. This technique involves an application of membrane filtered agar and allows the use of an image analysis system for observations of aggregates down to the size of individual cells. Embedding in agar is not satisfactory for microtome sectioning of microbial aggregates. Instead of the previously studied method of embedding in paraffin, embedding in glycol methacrylate resin has been found more advantageous. The latter technique is much simpler and provides better, unperturbed specimens.

Selectivity of layered double hydroxides and their derivative mixed metal oxides as sorbents of hydrogen sulfide.

In the context of finding high efficient sorbent materials for removing hydrogen sulfide (H2S) from air stream, a screening study was performed to find the best combination of metals for the synthesis of layered double hydroxides (LDHs) and their derivative mixed metal oxides. Based on selectivity of 998 natural mineral species of sulfur-containing compounds, Cu(2+), Ni(2+) and Zn(2+) were selected as divalent metals, and Fe(3+), Al(3+) and Cr(3+) as trivalent metals to synthesis the LDHs sorbents. 10 LDHs materials and their calcined mixed metal oxides, Ni(0.66)Al(0.34), Cu(0.35)Ni(0.32)Al(0.33), Zn(0.66)Al(0.34), Cu(0.36)Zn(0.32)Al(0.32), Ni(0.64)Fe(0.36), Cu(0.35)Ni(0.31)Fe(0.34), Ni(0.66)Cr(0.34), Cu(0.35)Ni(0.31)Cr(0.34), Zn(0.66)Cr(0.34), Cu(0.33)Zn(0.32)Cr(0.35) were synthesized, characterized chemically and physically, and then tested using breakthrough test to determine their sulfur uptake. Ni(0.64)Fe(0.36) mixed metal oxides was found to have the best uptake of hydrogen sulfide (136 mg H₂S/g). Regeneration of spent Ni(0.64)Fe(0.36) mixed metal oxides was studied using two different mixture solutions, NaCl/NaOH and acetate-buffer/NaCl/NaOH. The latter mixture successfully desorbed the sulfur from the Ni0.64Fe0.36 sorbent for 2 cycles of regeneration/sorption.

Performance of aerated submerged biofilm reactor packed with local scoria for carbon and nitrogen removal from municipal wastewater

An up-flow submerged biofilm reactor packed with scoria was evaluated for municipal wastewater treatment. The reactor was operated two cycles (with and without effluent recycle) as single aerobic reactor at hydraulic loading rate (HLR) of 3.5-4.0 L/L/day and four cycles (with and without effluent recycle) as anaerobic/aerobic reactor at two HLR (3.5 and 5.2 L/L/day). Results indicated better removal efficiency in case of anaerobic/aerobic cycles especially for ammonia and total nitrogen. Effluent recycling in the aerobic reactor enhanced ammonification with significant reduction in ammonia and nitrogen removal, while in case of single anaerobic/aerobic reactor the effluent recycling improved ammonia and nitrogen removal and kept nitrate concentration in the final effluent below 10 mg N/L. The reactor produced good settled sludge with sludge volume index (SVI) of 46-74 ml/g for aerobic cycles and 18-50 ml/g for anaerobic/aerobic cycles. The average sludge production was 0.145 g TSS/g COD removed.

HEAVY METAL DESORPTION STUDIES ON THE ARTIFICIALLY CONTAMINATED AL-QATIF SOIL

In this study, the relevance of mineralogy on the desorption capacities of Cu +2 and Pb +2 from artificially contaminated Al-Qatif soil has been investigated. The desorption capacities of both Cu +2 and Pb +2 using ethylenediaminetetraacetate (EDTA) as decontaminating solution are determined. The effect of decontaminating solution dosage and liquid to solid ratio on desorption capacities are examined. Under identical conditions, the removal efficiency of Pb +2 ions are found to higher than Cu +2 ions. This has been attributed mainly due to the differences in surface charges of specific retention sites which hold these metal ions. Further, the heavy metal ion solubility and surface properties of respective clay minerals decide the desorption rate in soil systems as the pore fluid pH reaches the heavy metal solubility range or point of zero charge of the clay minerals. These studies provide valuable insight with regards to their applicability as potential barrier materials for containing industrial leachates.

Retention studies on arsenic from aqueous solutions by lime treated semi arid soils

In this study, locally available semi-arid soils (Al-Ghat and Al-Qatif) having different chemical and mineralogical characteristics are considered as barrier materials, and their response to arsenic adsorption at varying initial concentrations, pH conditions, temperature and dilution ratios is studied. Empirical models (Langmuir and Freundlich) are applied to ascertain monolayer or heterogeneous adsorption. Lime is added to these soils in order to enhance their geotechnical properties. Kinetic models are employed to validate the type and nature of arsenic sorption onto these soils (whether pseudo first-order or second-order). Also Elovich and intraparticle diffusion models revealed that along with surface adsorption, chemisorptions and diffusion are the other processes occurring concurrently in the system, but it was not able to identify the dominant phenomenon among these models. It was concluded that both AlGhat and AlQatif soils when amended with lime can attenuate arsenic, and the experimental results correlate well with selected empirical models.

Performance of Soils and Soil Lime Mixtures as Liners to Retain Heavy Metal Ions in Aqueous Solutions

In this study, the relative performance of two soils after amending them with suitable matrices, in retaining the heavy metal ions has been evaluated. Al-Ghat soil and Al-Qatif soil of Saudi Arabia were mixed with different percentages of lime. Heavy metal ions such as copper and chromium were used to carry out sorption studies. Experimental data was used to plot adsorption isotherms. Langmuir isotherm was found to be more suitable than Freundlich isotherm for all soil mixtures. It can be concluded that Al-Qatif soil lime mixture can be used as a filter material and Al-Ghat soil lime mixture as the main liner material to attenuate selected heavy metals.

Enhanced sulfur removal by a tuned composite structure of Cu, Zn, Fe, and Al elements

Several combinations of high sulfur affinity elements of Cu, Zn, Fe, and Al were used to prepare sorbent materials that remove hydrogen sulfide (H2S) from air contaminated streams. The combination of these four elements in composite crystallinity structure resembling hydrotalcite-like and aurichalcite-like compounds showed excellent H2S uptake. Further tuning of the relative ratio among these elements resulted in outstanding H2S uptake. XRD revealed that the final sorbent material was featured by crystallinity structure that had two adjacent lower reflection angles. The experimental test showed H2S uptake was around 39% of the sorbent material weight when the concentration of H2S in the outlet was less than 0.5% of its concentration in the inlet. The sorbent material showed high sulfur removal efficiency at ambient temperature without prior calcination.