The Cost Benefit of Refinery Effluent Pretreatment Upstream of Membrane Bioreactors.

The established classical method of treating oil refinery effluent is flotation followed by biological treatment. Membrane bioreactors (MBRs) offer more advanced treatment, producing a clarified and potentially reusable treated effluent, but demand robust pretreatment to remove oil and grease (O&G) down to consistent, reliably low levels. An analysis of a full-scale conventional oil refinery ETP (effluent treatment plant) based on flotation alone, coupled with projected performance, energy consumption and costs associated with a downstream MBR, have demonstrated satisfactory performance of flotation-based pretreatment. The flotation processes, comprising an API (American Petroleum Institute) separator followed by dissolved air flotation (DAF), provided ~90% removal of both total suspended solids (TSS) and O&G coupled with 75% COD (chemical oxygen demand) removal. The relative energy consumption and cost of the pretreatment, normalised against both the volume treated and COD removed, was considerably less for the API-DAF sequence compared to the MBR. The combined flotation specific energy consumption in kWh was found to be almost an order of magnitude lower than for the MBR (0.091 vs. 0.86 kWh per m3 effluent treated), and the total cost (in terms of the net present value) around one sixth that of the MBR. However, the nature of the respective waste streams generated and the end disposal of waste solids differ significantly between the pretreatment and MBR stages.

A Brief Review of the Status of Low-Pressure Membrane Technology Implementation for Petroleum Industry Effluent Treatment.

Low-pressure membrane technology (ultrafiltration and microfiltration) has been applied to two key effluents generated by the petroleum industry: produced water (PW) from oil exploration, a significant proportion being generated offshore, and onshore refinery/petrochemical effluent. PW is treated physicochemically to remove the oil prior to discharge, whereas the onshore effluents are often treated biologically to remove both the suspended and dissolved organic fractions. This review examines the efficacy and extent of implementation of membrane technology for these two distinct applications, focusing on data and information pertaining to the treatment of real effluents at large/full scale. Reported data trends from PW membrane filtration reveal that, notwithstanding extensive testing of ceramic membrane material for this duty, the mean fluxes sustained are highly variable and generally insufficiently high for offshore treatment on oil platforms where space is limited. This appears to be associated with the use of polymer for chemically-enhanced enhanced oil recovery, which causes significant membrane fouling impairing membrane permeability. Against this, the application of MBRs to onshore oil effluent treatment is well established, with a relatively narrow range of flux values reported (9−17 L·m−2·h−1) and >80% COD removal. It is concluded that the prospects of MBRs for petroleum industry effluent treatment are more favorable than implementation of membrane filtration for offshore PW treatment.

An empirical determination of the whole-life cost of FO-based open-loop wastewater reclamation technologies.

Over the past 5-10 years it has become apparent that the significant energy benefit provided by forward osmosis (FO) for desalination arises only when direct recovery of the permeate product from the solution used to transfer the water through the membrane (the draw solution) is obviated. These circumstances occur specifically when wastewater purification is combined with saline water desalination. It has been suggested that, for such an "open loop" system, the FO technology offers a lower-cost water reclamation option than the conventional process based on reverse osmosis (RO). An analysis is presented of the costs incurred by this combined treatment objective. Three process schemes are considered combining the FO or RO technologies with membrane bioreactors (MBRs): MBR-RO, MBR-FO-RO and osmotic MBR (OMBR)-RO. Calculation of the normalised net present value (NPV/permeate flow) proceeded through developing a series of empirical equations based on available individual capital and operating cost data. Cost curves (cost vs. flow capacity) were generated for each option using literature MBR and RO data, making appropriate assumptions regarding the design and operation of the novel FO and OMBR technologies. Calculations revealed the MBR-FO-RO and OMBR-RO schemes to respectively offer a ∼20% and ∼30% NPV benefit over the classical MBR-RO scheme at a permeate flow of 10,000 m3  d-1, provided the respective schemes are applied to high and low salinity wastewaters. Outcomes are highly sensitive to the FO or OMBR flux sustained: the relative NPV benefit (compared to the classical system) of the OMBR-RO scheme declined from 30% to ∼4% on halving the OMBR flux from a value of 6 L m-2. h-1.

Carbonaceous and nitrogenous disinfection by-product formation from algal organic matter.

Seasonal algal blooms in drinking water sources release intracellular and extracellular algal organic matter (AOM) in significant concentrations into the water. This organic matter provides precursors for disinfection by-products (DBPs) formed when the water is subsequently chlorinated at the final disinfection stage of the potable water treatment process. This paper presents results of AOM characterisation from five algal species (three cyanobacteria, one diatom and one green) alongside the measurement of the DBP formation potential from the AOM of six algal species (an additional diatom). The character was explored in terms of hydrophilicity, charge and protein and carbohydrate content. 18 DBPs were measured following chlorination of the AOM samples: the four trihalomethanes (THMs), nine haloacetic acids (HAAs), four haloacetonitriles (HANs) and one halonitromethane (HNM). The AOM was found to be mainly hydrophilic (52 and 81%) in nature. Yields of up to 92.4 µg mg-1 C carbonaceous DBPs were measured, with few consistent trends between DBP formation propensity and either the specific ultraviolet absorbance (SUVA) or the chemical characteristics. The AOM from diatomaceous algae formed significant amounts of nitrogenous DBPs (up to 1.7 µg mg-1 C). The weak trends in DBPFP may be attributable to the hydrophilic nature of AOM, which also makes it more challenging to remove by conventional water treatment processes.

Coagulant recovery and reuse for drinking water treatment.

Coagulant recovery and reuse from waterworks sludge has the potential to significantly reduce waste disposal and chemicals usage for water treatment. Drinking water regulations demand purification of recovered coagulant before they can be safely reused, due to the risk of disinfection by-product precursors being recovered from waterworks sludge alongside coagulant metals. While several full-scale separation technologies have proven effective for coagulant purification, none have matched virgin coagulant treatment performance. This study examines the individual and successive separation performance of several novel and existing ferric coagulant recovery purification technologies to attain virgin coagulant purity levels. The new suggested approach of alkali extraction of dissolved organic compounds (DOC) from waterworks sludge prior to acidic solubilisation of ferric coagulants provided the same 14:1 selectivity ratio (874 mg/L Fe vs. 61 mg/L DOC) to the more established size separation using ultrafiltration (1285 mg/L Fe vs. 91 mg/L DOC). Cation exchange Donnan membranes were also examined: while highly selective (2555 mg/L Fe vs. 29 mg/L DOC, 88:1 selectivity), the low pH of the recovered ferric solution impaired subsequent treatment performance. The application of powdered activated carbon (PAC) to ultrafiltration or alkali pre-treated sludge, dosed at 80 mg/mg DOC, reduced recovered ferric DOC contamination to <1 mg/L but in practice, this option would incur significant costs. The treatment performance of the purified recovered coagulants was compared to that of virgin reagent with reference to key water quality parameters. Several PAC-polished recovered coagulants provided the same or improved DOC and turbidity removal as virgin coagulant, as well as demonstrating the potential to reduce disinfection byproducts and regulated metals to levels comparable to that attained from virgin material.

Acidified and ultrafiltered recovered coagulants from water treatment works sludge for removal of phosphorus from wastewater.

This study used a range of treated water treatment works sludge options for the removal of phosphorus (P) from primary wastewater. These options included the application of ultrafiltration for recovery of the coagulant from the sludge. The treatment performance and whole life cost (WLC) of the various recovered coagulant (RC) configurations have been considered in relation to fresh ferric sulphate (FFS). Pre-treatment of the sludge with acid followed by removal of organic and particulate contaminants using a 2kD ultrafiltration membrane resulted in a reusable coagulant that closely matched the performance FFS. Unacidified RC showed 53% of the phosphorus removal efficiency of FFS, at a dose of 20 mg/L as Fe and a contact time of 90 min. A longer contact time of 8 h improved performance to 85% of FFS. P removal at the shorter contact time improved to 88% relative to FFS by pre-acidifying the sludge to pH 2, using an acid molar ratio of 5.2:1 mol H(+):Fe. Analysis of the removal of P showed that rapid phosphate precipitation accounted for >65% of removal with FFS. However, for the acidified RC a slower adsorption mechanism dominated; this was accelerated at a lower pH. A cost-benefit analysis showed that relative to dosing FFS and disposing waterworks sludge to land, the 20 year WLC was halved by transporting acidified or unacidified sludge up to 80 km for reuse in wastewater treatment. A maximum inter-site distance was determined to be 240 km above the current disposal route at current prices. Further savings could be made if longer contact times were available to allow greater P removal with unacidified RC.

Occurrence and fate of pharmaceutical and personal care products in a sewage treatment works.

The occurrence and fate of eight pharmaceutical and personal care products (PPCPs) during sewage treatment has been studied in a pilot-scale treatment plant, comprising a primary settler (2.85 m(3)), an aeration tank (1.845 m(3)) and a secondary clarifier (0.5 m(3)), placed on site at a wastewater treatment works in the north west of the UK. It was fed both with raw sewage and the return liquor produced after sludge centrifugation, thus representing the most common configuration for a municipal sewage treatment plant based on the activated sludge process. Samples were taken at six different locations, including the return liquor stream, and analysed for musk fragrances and pharmaceutically active compounds belonging to various therapeutic groups such as anti-inflammatory drugs, tranquillisers and antiepileptics. Mass balances were conducted for those PPCPs that were quantifiable. The fate of the PPCPs was found to differ according to their physical-chemical characteristics. Anti-inflammatories underwent a degradation process and were almost completely removed from sewage during the biological treatment step. Musk fragrances were only partially removed, through adsorption onto the primary suspended solids and the biomass in the aerobic process, due to their strong lipophilic characteristics. The results of this study provide increasing evidence that the partial removal of these substances through the sewage treatment process contribute to the environmental occurrence of PPCPs. Consequently, existing STPs should be upgraded in order to attenuate the release of these substances into the aquatic environment.

Fate and impact of organics in an immersed membrane bioreactor applied to brine denitrification and ion exchange regeneration.

The application of membrane bioreactors (MBRs) to brine denitrification for ion exchange regeneration has been studied. The developed culture was capable of complete brine denitrification at 50 gNaCl.l(-1). Denitrification reduced to c.60% and c.70% when salinity was respectively increased to 75 and 100g.l(-1), presumed to be due to reduced growth rate and the low imposed solids retention time (10 days). Polysaccharide secretion was not induced by stressed cells following salt shocking, implying that cell lysis did not occur. Fouling propensity, monitored by critical flux, was steady at 12-15l.m(-2).h(-1) during salinity shocking and after brine recirculation, indicating that the system was stable following perturbation. Low molecular weight polysaccharide physically adsorbed onto the nitrate selective anion exchange resin during regeneration reducing exchange capacity by c.6.5% when operating up to complete exhaustion. However, based on a breakthrough threshold of 10 mgNO(3)(-)-N.l(-1) the exchange capacity was comparative to that determined when using freshly produced brine for regeneration. It was concluded that a denitrification MBR was an appropriate technology for IEX spent brine recovery and reuse.

Character of extracellular polymeric substances and soluble microbial products and their effect on membrane hydraulics during airlift membrane bioreactor applications.

The effect of extracellular polymeric substances and soluble microbial products developed from wastewater and mature landfill leachate biomass was assessed using a pilot-scale membrane bioreactor operating polymeric and ceramic air-lift sidestream multichannel membranes. The plant was operated under identical conditions of sludge retention time, system hydrodynamics ,and parity of food-to-microorganism ratios. Biomass samples were extracted and fractionated (fixed and bound material, carbohydrate and protein extracts) and chemically and physically analyzed with the feedwaters. Both ceramic and polymeric membranes were tested and the critical flux (J(C)) determined according to the classical flux-step analysis. Although permeability (K) of both materials reduced with increasing flux (J), the ceramic material had a higher resistance to fouling, demonstrating a higher K (by a factor of 1.2 and 3.2 for wastewater and leachate, respectively, at J of 30 L x m(-2) x h(-1)) and lower fouling rate (dP/dt) (by more than an order of magnitude at the same J) than the polymeric membrane. Evidence suggests that deterioration of membrane permeability resulting from leachate biomass arises from the feedwater itself, rather than the products derived from the biomass, and that colloidal and/or soluble total organic carbon is primarily responsible for it.

Denitrification from drinking water using a membrane bioreactor: chemical and biochemical feasibility.

Interest is growing in developing membrane bioreactors (MBRs) to replace ion exchange for nitrate removal from drinking water. However, few published studies have successfully managed to retain exogenous or biologically derived carbon. This study determined an optimum C:N by substrate breakthrough rather than maximum nitrate removal. By dosing

Influence of substrate on fouling in anoxic immersed membrane bioreactors.

The influence of carbon substrate chemistry on membrane bioreactor (MBR) fouling in anoxic conditions has been evaluated. The use of a weak carboxylic acid (acetic acid) resulted in the production of large open-floc structures (up to 508microm) that were susceptible to breakage. Primary particles (d(10) and d(20) particle sizes, 5.5+/-1.3 and 15.3+/-8.2microm, respectively) and macromolecular soluble microbial products (SMPs) were generated, directly impacting on membrane fouling. The use of a primary alcohol (ethanol), on the other hand, encouraged the growth of flocs similar to activated sludge. These flocs produced low concentrations of primary particles (d(10) and d(20) particle sizes, 120.6+/-36.1 and 185.2+/-62.7microm, respectively) and high-molecular-weight SMP, and the particles had sufficient mechanical integrity to withstand shear. Consequently, the use of ethanol resulted in sufficient suppression of fouling to extend the filtration time by a factor of three. An increase in MLSS concentration did not directly impact upon fouling when operating with ethanol, primarily because of the low concentration of particulate matter produced.

Bacterial diversity is determined by volume in membrane bioreactors.

It has been proposed that established models and theories developed in classical ecology could be employed to greatly improve the optimization of wastewater treatment plants (WWTP) by placing the microbiological component onto a model-predictive basis. In particular, this could be achieved by better understanding bacterial community assembly and development. The species-area relationship is one of the oldest biological laws and has been used to describe spatial diversity patterns in contiguous habitats and on islands. In the current study, bacterial communities in seven membrane bioreactors (MBR), of increasing size, located across the UK were sampled. A significant linear relationship between bacterial taxa richness and reactor size was observed and was similar to classical species-area relationships of larger organisms colonizing oceanic islands. Rank-abundance plots revealed a gradient of greater evenness in community structure as MBR volume increased. Application of the Raup and Crick probability-based similarity index indicated a strong role for dispersal in MBR colonization and community structure. Our findings demonstrate that the MBR sampled behaved like islands with respect to bacterial colonization in accordance with the theory of island biogeography. In addition this study provides further evidence that biodiversity at the bacterial level is more similar to that of animals and plants than previously postulated.

Critical analysis of submerged membrane sequencing batch reactor operating conditions.

To evaluate the Submerged Membrane Sequencing Batch Reactor process, several short-term studies were conducted to define critical flux, membrane aeration and intermittent filtration operation. Critical flux trials indicated that as mixed liquor suspended solids increased in concentration so would the propensity for membrane fouling. Consequently in order to characterise the impact of biomass concentration increase (that develops during permeate withdrawal) upon submerged microfiltration operation, two longer term studies were conducted, one with a falling hydraulic head and another with a continuous hydraulic head (as in membrane bio-reactors). Trans membrane pressure data was used to predict the maximum possible operating periods at 10 and 62 days for the falling hydraulic head and continuous hydraulic head respectively. Further analysis revealed that falling hydraulic head operation would require 21% more aeration to maintain a consistent crossflow velocity than continuous operation and would rely on pumping for full permeate withdrawal 80% earlier. This study concluded that further optimisation would be required to make this technology technically and economically viable.