Reduced Low-Pressure Membrane Fouling by Inline Coagulation Pretreatment for a Colored River Water.

Drinking water treatment (DWT) using low-pressure membranes (LPM) has become increasingly popular due to their many reported advantages compared to conventional technologies. Productivity decline due to fouling has prevented LPMs from becoming the technology of choice in DWT, however, coagulation pretreatment either with or without particle separation mitigates fouling phenomena. The effectiveness of coagulation/flocculation/sedimentation (CF-S), coagulation/flocculation/dissolved air flotation (CF-DAF), and inline coagulation (CF-IN) as technologies for pretreatment of feed water has rarely been investigated using the same water source. In this study, CF-S, CF-DAF, and CF-IN are directly compared as pretreatment of a tubular multi-channeled ultrafiltration (UF) membrane using the same highly colored river water. Three-day long filtration tests were performed using an automated bench-scale filtration apparatus with an inside-out configuration. Although CF-DAF had the greatest removal of dissolved organic matter (DOM) and hydrophobic organics, CF-S pretreatment resulted in a similar level of total fouling. Compared to CF-DAF and CF-S, CF-IN pretreatment resulted in lower fouling. The hydraulic and chemical reversibility of CF-IN fouling was seen to be strongly influenced by the feed water zeta potential, suggesting the importance of floc electrostatic and morphological characteristics on inline coagulation performance.

Flux Increase Occurring When an Ultrafiltration Membrane Is Flipped from a Normal to an Inverted Position-Experiments and Theory.

The effects of flipping membranes with hydrophilic/hydrophobic asymmetry are well documented in the literature, but not much is known on the impact of flipping a membrane with dense/porous layer asymmetry. In this work, the pure water flux (PWF) of a commercial polyethersulfone (PES) membrane and a ceramic ultrafiltration (UF) membrane was measured in the normal and inverted positions. Our experimental results showed that the PWF was two orders of magnitude higher when the PES membrane was flipped to the inverted position, while the increase was only two times for the ceramic membrane. The filtration experiments were also carried out using solutions of bovine serum albumin and poly(vinylpyrrolidone). A mathematical model was further developed to explain the PWF increase in the inverted position based on the Bernoulli's rule, considering a straight cylindrical pore of small radius connected to a pore of larger radius in series. It was found by simulation that a PWF increase was indeed possible when the solid ceramic membrane was flipped, maintaining its pore geometry. The flow from a layer with larger pore size to a layer with smaller pore size occurred in the backwashing of the fouled membrane and in forward and pressure-retarded osmosis when the membrane was used with its active layer facing the draw solution (AL-DS). Therefore, this work is of practical significance for the cases where the direction of the water flow is in the inverted position of the membrane.

Large batch bench-scale dissolved air flotation system for simulating full-scale turbidity removal.

One of the expected outcomes of global warming is increased algal and cyanobacterial blooms. Based on its ability to separate algal particles, dissolved air flotation (DAF) is considered as a climate change adaptation technology for water treatment. The feasibility of DAF treatment is often assessed using DAF jar tests; however, they are not particularly good at predicting a full-scale DAF system's turbidity removals. Therefore, our group has developed a more reliable larger-diameter/larger-volume batch apparatus (LB-DAF), which was optimized by comparison with a full-scale DAF plant treating a low turbidity, highly coloured river water (SUVA ∼ 4.3). The objective of this study was to verify that the LB-DAF was capable of simulating full-scale DAF systems treating two significantly different waters. One was water from a large eutrophic bay in Lake Ontario (SUVA ∼2.6) and the second was a river water (SUVA ∼3.5). The turbidity removals achieved by the full-scale DAF systems treating these waters were compared with those for the LB-DAF tests conducted using different flocculation velocity gradients, saturated water pressures, recycle ratios and water depth to diameter ratios. The LB-DAF tests are good predictors of the full-scale DAF turbidity removals, the average difference for the two waters tested were 2% and 6%. The LB-DAF natural organic matter (NOM) removals for both waters differed by less than 1% from that measured at the corresponding treatment plants. In addition, as in our previous LB-DAF study, varying the different LB-DAF operational variables did not have a significant impact on turbidity and NOM removals.

Investigation of settleability of biologically produced solids and biofilm morphology in moving bed bioreactors (MBBRs).

The objective of this work is to investigate the effects of surface area loading rates (SALRs) and hydraulic retention times (HRTs) in moving bed bioreactor (MBBR) systems on the morphology and thickness of the attached biofilm along with subsequent effects on particle size distribution and the settling characteristics of the biologically produced solids. The morphology of biofilm attached to the MBBR carriers changed from a porous biofilm to a biofilm with a more filamentous structure throughout the study at various operating conditions without observable correlation with SALR and HRT. Although, biofilm morphology did not demonstrate an effect on the biologically produced solids observed in this study, the thinnest biofilms resulted in the highest concentration of solids in the effluent. Furthermore, the particle size distribution analysis demonstrated that both higher SALRs and longer HRTs resulted in a shift towards larger-sized particles. Increases in SALR and HRT, independent of each other, also showed increases in effluent solid concentration and lower settleability of the solids.

A new computational control strategy for leachate management in bioreactor landfills.

A novel computational measurement-based control strategy (CMCS) was developed to manage leachate recirculation based on monitoring ofkey system parameters. The proposed framework identifies the operational phase ofthe controlled bioreactor, and accordingly determines quantities ofleachate, buffer, supplemental water, and nutritional amendments required to provide the temporally changing landfill microbial consortia with their growth requirements. The CMCS was tested in a pilot-scale bioreactor cell (0.5 m3) for a period of nine months, and compared to a conventional open-loop leachate control scheme (fixed recirculation rate of produced leachate) in an identical cell. Overall, positive results confirmed the applicability and benefits of the control strategy to optimize the leachate recirculation and manipulation processes. Throughout the 21 operational cycles of the controlled bioreactor cell, the maximum specific daily recirculation volume (24 L/t/d) was sixfold the minimum volume determined. The amounts of inoculum/nutrient, buffer, and supplemental water were also computed cyclically, and ranged between 2% and 11%, 1% and 9%, and 3% and 16% of the total volume recycled, respectively. The recirculated volumes of leachate and other amendments were highly variable, and did not follow any predictable trends. In general, CMCS achieved proper control with a minimal use of resources, e.g. it utilized about 55% less buffer compared with the leachate neutralization practice commonly used in lab- and pilot-scale studies. The greater degradation rates of organic matter combined with relative increases in biogas production (1.7-fold greater) demonstrate that calculation-based recirculation stimulated the methanogenic activity and accelerated the bioreactor evolution.

Influence of supplemental heat addition on performance of pilot-scale bioreactor landfills.

Implementation of supplemental heat addition as a means of improving bioreactor landfill performance was investigated. The experimental work was conducted with two pilot-scale bioreactor setups (control cell and heated cell) operated for 280 days. Supplemental heat was introduced by recirculating leachate heated up to 35 °C compared to the control which used similar quantities of leachate at room temperature (21 ± 1 °C). The temporal and spatial effects of recirculating heated leachate on the landfill internal temperature were determined, and performance was assessed in terms of leachate parameters and biogas production. Recirculation of heated leachate helped establish balanced anaerobic microbial consortia that led to earlier (70 days) and greater (1.4-fold) organic matter degradation rates, as well as threefold higher methane production compared to the non-heated control. Despite the significant enhancements in performance resulting from supplemental heat addition, heated leachate recirculation did not significantly impact waste temperatures, and the effects were mainly restricted to short periods after recirculation and mostly at the upper layers of the waste. These findings suggest that improvements in bioreactor landfill performance may be achieved without increasing the temperature of the whole in-place waste, but rather more economically by raising the temperature at the leachate/waste interface which is also exposed to the maximum moisture levels within the waste matrix.

Electrochemical regeneration of field spent GAC from two water treatment plants.

The effectiveness of on-site thermal regeneration of field-spent granular activated carbon (GAC) from two municipal drinking water facilities was compared with bench-scale electrochemical regeneration, a novel regeneration technology. The regeneration method was evaluated using aqueous natural organic material (NOM) adsorption, iodine number analysis, and surface area analysis. In contrast to the large electrochemical regeneration efficiencies reported in the literature for GAC loaded with phenolics and other individual organic compounds, the electrochemical reactor tested was only able to regenerate 8-15% of the NOM adsorption capacity of the field spent GAC. In contrast, thermal reactivation achieved up to 103% regeneration efficiency. To more accurately assess the efficiency of regeneration processes for water treatment applications, GAC should be loaded in continuous-flow columns and not batch rectors. The iodine number analysis yielded higher efficiency values, however it did not give an accurate estimate of the regeneration efficiency. The small changes in GAC pore size distribution were consistent with the low electrochemical regeneration efficiencies. These low efficiencies appear to be related to the low reversibility of NOM adsorption and to pH-induced adsorbate desorption being the primary mechanism for this type of electrochemical regeneration system.

Embriología

Generalidades. Fecundación y segmentación. Período presomítico. Período somítico. Anatomía del embrión de la quinta semana. Morfogénesis tardía. Histogénesis. Mecanismo del desarrollo. Nociones elementales de genética médica. Malformaciones congénitas