Dialysis Pretreatment Research Articles

Culturing strategy for producing levan by upcycling oil produced water effluent as base medium for Zymomonas mobilis

Three distinct reported media were tested as organic and inorganic supplementation of produced water (PW) from mature oil wells with the aim of producing levan. This effluent is generated at high amounts during oil extraction and are often associated to significant environmental impact and treatment costs. PW may display significant amounts of salts that can hinder microbial growth. Using a high saline PW (8%) this research identified that higher sucrose concentrations in association with ammonium and magnesium sulfates mitigated the negative effect of high salts concentrations on Zymomonas mobilis production of levan. Using neat supplemented PW as medium generated within 24 h 10 g L−1 of levan. The highest production of 31.9 g L−1 was obtained with dialyzed pretreated PW. Dialysis pretreatment may be an important standardization of PW prior to full-scale application. FT-IR characterization shows no significant differences between the produced levan and the commercial counterpart.

Dialysis as a new pre-treatment technique for online bacterial counting

Real-time bacteriological counting technology is capable of providing an online profile of bacterial removal during the wastewater treatment process, and can enhance the safety of recycled water for potable water reuse. However, autofluorescence emanating from dissolved organic compounds present in treated wastewater interferes with the analysis. In this study, a novel approach is adopted, viz., dialysis treatment for the removal of dissolved interfering substances from treated wastewater, and the efficiency of this treatment protocol is evaluated as a pre-treatment technique for real-time bacteriological counting. Dialysis using membranes having a molecular weight cut-off (MWCO) of 1000 kDa and 6–8 kDa were found to successfully reduce the intensity of autofluorescence emitted from the interfering substances; whereas the courser dialysis membrane having a MWCO of 1000 kDa was found to be more effective in removing the interfering substances. Here we demonstrate for the first time that continuous online dialysis treatment aids in the direct determination of the bacterial counts in ultrafiltration- and membrane bioreactor-treated wastewaters. The results of the study indicate that the dialysis pre-treatment technique is effective for continuously reducing the concentration of interfering substances in treated wastewater, and thus allows for direct online counting of bacteria.

A modified method of high molecular weight adsorbable organic chlorine measurement in saline water: Dialysis pretreatment

Adsorbable organic halogen is a mean to quantify total organic halogen, which is an important toxicity indicator in disinfection byproduct studies. However, quantification of low concentrations of adsorbable organic chlorine (AOCl) formation in seawater chlorination using the USEPA Method 9020B was found inaccurate due to the presence of high concentrations of chloride. In this study, a dialysis-based pretreatment technique was proposed, optimized and adopted to eliminate the interference of chloride in quantifying low concentrations of AOCl in seawater. A volumetric ratio of dialysis samples to continuous-flow deionized water at 1:1200 was found sufficient to remove over 99% of chloride. As a result, chloride to AOCl ratios can be reduced to less than 20,000, and the interference from chloride can thus be eliminated. The detainment of AOCl by the dialysis pretreatment depends on the molecular weight cutoff of the cellulose seamless dialysis membrane currently used, which was determined to be around 320 to 500 Da. The dialysis pretreatment can be used to measure AOCl concentrations in chlorinated seawater samples at pH 6.5 to 10.

Dialysis Pretreatment for Dissolved Organic Nitrogen Analysis in Freshwaters

Total dissolved nitrogen (TDN), including dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON), plays an important role in numerous environmental processes, such as nutrient cycling and lake and estuary eutrophication. The impact of DIN on environmental processes has been extensively studied. However, the understanding on DON in the environment is largely unknown, as there is no direct method for DON measurement. In practice, DON was determined by subtracting DIN from TDN. Large measurement errors could be induced when DIN becomes dominant in sample. This study was to investigate the impact of two pretreatments of dialysis, dialysis against Millipore water and dialysis against phosphate buffer (4.7 mM H3PO4-5.3 mM KH2PO4, pH 2.2) using a cellulose ester (CE) membrane (100–500 Da molecular weight cutoff), on DON measurement in a broad DIN range from various aquatic ecosystems. Results showed that the removal of NH4-N and NO3-N by both dialysis approaches was highly effective (>80%), but the DON loss by the former was significantly lower than by the latter. This study demonstrated that dialysis against Millipore water with the membrane would be more effective as a sample pretreatment for DIN removal, leading to a reliable and accurate DON measurement.

Measurements of Dissolved Organic Nitrogen in Wastewater Samples with Nanofiltration Pretreatment

Conventional dissolved organic nitrogen (DON) measurements for water samples with high dissolved inorganic nitrogen (DIN) to total dissolved nitrogen (TDN) ratio are incorrect due to the cumulative analytical errors of independently measured nitrogen species (DIN and TDN). In this study, we present a nanofiltration (NF) pretreatment to increase the accuracy and precision of DON measurements by selectively concentrating DON while passing through DIN species in water samples to reduce the DIN/TDN ratio. Compared to the available dialysis pretreatment method, the NF pretreatment method shows a similar improved performance for DON measurement for aqueous samples and can save at least 20 h of operating time and a large volume of deionized water, which is beneficial for laboratories involved in DON analysis. To prove the feasibility of the pretreatment, we collected and compared effluent samples from two sewage water treatment plants. The result shows that with the pretreatment, the DIN to TDN ratio has significantly decreased while the dissolved organic carbon (DOC) recovery has been increased. So this NF pretreatment is available.

Dialysis is superior to anion exchange for removal of dissolved inorganic nitrogen from freshwater samples prior to dissolved organic nitrogen determination

Environmental context Aquatic ecosystem health may be adversely affected by dissolved organic nitrogen pollution, and accurate analytical techniques are needed to assess these effects. Our study shows that dialysis is the best sample pre-treatment technique to increase the accuracy of dissolved organic nitrogen determination. It will improve analysis and understanding of the role of dissolved organic nitrogen in the nitrogen cycle of affected aquatic ecosystems. Abstract Dissolved organic nitrogen (DON) is usually determined as the difference between total dissolved nitrogen (TDN) and dissolved inorganic nitrogen (DIN). When applying this approach to samples with high DIN concentrations, there is a risk that small relative errors in TDN and DIN measurements may propagate into high absolute errors of the determined DON concentration. To reduce such errors, two pre-treatment methods have been suggested for the removal of DIN before the determination of DON: anion-exchange pre-treatment (AEP) and dialysis pre-treatment (DP). In this study, we tested the suitability of AEP and DP for DIN removal in order to increase the accuracy of DON determination of freshwater samples. The AEP performed well for standard compounds, yielding high dissolved organic carbon (DOC) recovery rates and >99 % removal of nitrate, whereas DON recovery rates varied and no removal occurred for ammonium and nitrite. However, AEP proved not to be suitable for natural samples, as it removed 36–74 % DOC and up to 83 % DON. In contrast, after 72 h of DP, 17–32 % DOC and DON had been removed from the natural samples, whereas >98 % nitrate was removed in all but one case, and >87 % of the ammonium and nitrite were removed. Moreover, we found that DP results in a significant increase in DON determination accuracy. In conclusion, DP is a useful measure to increase DON determination accuracy in natural freshwater samples with high DIN-to-TDN ratios, whereas AEP is not recommended for DON determination of natural freshwater samples.

Measurements of dissolved organic nitrogen (DON) in water samples with nanofiltration pretreatment

Dissolved organic nitrogen (DON) measurements for water samples with a high dissolved inorganic nitrogen (DIN, including nitrite, nitrate and ammonia) to total dissolved nitrogen (TDN) ratio using traditional methods are inaccurate due to the cumulative analytical errors of independently measured nitrogen species (TDN and DIN). In this study, we present a nanofiltration (NF) pretreatment to increase the accuracy and precision of DON measurements by selectively concentrating DON while passing through DIN species in water samples to reduce the DIN/TDN ratio. Three commercial NF membranes (NF90, NF270 and HL) were tested. The rejection efficiency of finished water from the Yangshupu drinking water treatment plant (YDWTP) is 12%, 31%, 8% of nitrate, 26%, 28%, 23% of ammonia, 77%, 78%, 82% of DOC (dissolved organic carbon), and 83%, 87% 88% of UV 254 for HL, NF90 and NF270, respectively. NF270 showed the best performance due to its high DIN permeability and DON retention (∼80%). NF270 can lower the DIN/TDN ratio from around 1 to less than 0.6 mg N/mg N, and satisfactory DOC recoveries as well as DON measurements in synthetic water samples were obtained using optimized operating parameters. Compared to the available dialysis pretreatment method, the NF pretreatment method shows a similar improved performance for DON measurement for aqueous samples and can save at least 20 h of operating time and a large volume of deionized water, which is beneficial for laboratories involved in DON analysis. DON concentration in the effluent of different treatment processes at the YDWTP and the SDWTP (Shijiuyang DWTP) in China were investigated with and without NF pretreatment; the results showed that DON with NF pretreatment and DOC both gradually decreased after each water treatment process at both treatment plants. The advanced water treatment line, including biological pretreatment, clarification, sand filtration, ozone-BAC processes at the SDWTP showed greater efficiency of DON removal from 0.37 to 0.11 mg N L −1 than that at the YDWTP, including pre-ozonation, clarification and sand filtration processes from 0.18 to 0.11 mg N L −1.

Optimization of dissolved organic nitrogen (DON) measurements in aqueous samples with high inorganic nitrogen concentrations

Since dissolved organic nitrogen (DON) concentrations in aqueous samples can only be determined by the subtraction of three independently measured concentrations (total dissolved nitrogen (TDN), nitrate and ammonium), analytical errors are compounded in the calculation of DON concentration. Several methods were tested to increase the recovery and precision of the DON determinations in aqueous samples with high inorganic nitrogen concentrations. The first step was the objective selection of the most accurate TDN analysis method. The persulfate oxidation (PO) method had a significantly higher recovery than the high-temperature catalytic oxidation (HTCO) method. The second step involved the lowering of the DIN (dissolved inorganic N)/TDN ratio by applying three sample pretreatment procedures: conventional dialysis, dialysis against a buffered acceptor solution and concentration of the samples combined with the buffered dialysis. Despite the fact that DIN was only partially removed, conventional dialysis pretreatment resulted in higher precision and recovery of the DON determination compared to analysis of untreated samples. Dialysis of the samples against a buffered acceptor solution gave additional improvements in precision, recovery, and reproducibility. The concentration of aqueous samples by lyophilization, however, did not lead to higher recovery rates in the DON measurements.

Occurrence and removal of dissolved organic nitrogen in US water treatment plants

Two seasonal sampling campaigns of raw and finished waters from 28 water treatment plants were conducted to investigate the occurrence and removal of dissolved organic nitrogen (DON). A new dialysis pretreatment technique was applied for accurate DON determination. The average DON concentration was 0.186 mg/L nitrogen (N) in raw waters and 0.148 mg/L N in finished waters. On average, total dissolved nitrogen in the raw waters consist of 10% DON and 90% dissolved inorganic nitrogen. The dissolved organic carbon (DOC)‐to‐DON ratio of raw waters averaged 18 mg DOC to 1 mg DON. DON removal during water treatment closely mirrored that of DOC removal. The molecular weight distribution of DON roughly parallels that of DOC, and higher‐molecular‐weight fractions (> 10,000 D) of both DON and DOC were preferentially removed across the full‐scale water treatment plants.

Dissolved Organic Nitrogen Measurement Using Dialysis Pretreatment

Dissolved organic nitrogen (DON) is important for ecological and engineering researches. Quantification of low DON concentrations in waters with elevated dissolved inorganic nitrogen (DIN) using existing methods is inaccurate. In this study, a dialysis-based pretreatment technique was optimized and adopted to reduce the interference from DIN to the quantification of DON in natural water. A cellulose ester dialysis tube (nominal molecular weight cutoff = 100 Da) was used in batch and continuous-flow dialysis steps with model compounds, natural organic matter isolates, and bulk waters to develop a dialysis pretreatment approach that selectively reduces DIN from solutions containing DON. By reducing DIN concentrations, propagation of analytical variance in total dissolved nitrogen (TDN) and DIN species concentrations allows more accurate determination of DON (DON = TDN - NO3 - NO2- - NH3/NH4+). Dialysis for 24 h against continuously flowing distilled water reduced DIN species by 70%. With dialysis pretreatment, DON recoveries of more than 95% were obtained for surface water and finished drinking water, but wastewater experienced a slight loss (approximately 10%) of DON possibly due to the adsorption of organics onto the dialysis membrane, permeation of low molecular weight fractions, or biodegradation. Dialysis experiments using surface water spiked with different DIN/TDN ratios concluded that dialysis pretreatment leads to more accurate DON determination than no dialysis when DIN/TDN ratios exceed 0.6 mg of N/mg of N.

Simultaneous Determination of Small Cations and Anions by Capillary Electrophoresis

A capillary electrophoresis system for the simultaneous determination of small cations and anions has been developed. Cations and anions in a sample are separated in one single electrophoretic run using one capillary and just one detector. The sample is injected into the first end of the separation capillary and subsequently into the second end. When the high voltage is applied, the cations and the anions in the two injected sample portions start to migrate against each other toward the center of the capillary. The detection window is placed approximately in the middle of the capillary. A suitable electrolyte consists of 6 mM 4-aminopyridine, 2.7 mM H2CrO4, and 30 μM cetyltrimethylammonium bromide at pH 8. The composition of the background electrolyte provides excellent separation of 22 small inorganic and organic anions and 1A and 2A class cations within 5 min. The overall repeatability of the migration times is less than 0.3%, and the repeatability of the peak area ranges from 1.7 to 5.5% (n = 9) based on manual hydrodynamic injections with a duration of 40 s. The technique has been applied for the analysis of tap water, rainwater, and process water samples. The total time for an analysis of both cations and anions in a water sample is less than 3 min. Milk and mud samples were also analyzed after off-line dialysis pretreatment.

A modified method for determining available lysine in protein recovered from heat treated potato juice

A dialysis pretreatment to remove low molecular weight interfering compounds from potato protein water prior to measuring its lysine availability is described. After dialysis the ϵ-trinitrophenyl- l-lysine showed excellent correlation with the magnitude of heat treatment the protein water received. Conversely, analysis of the same sample without pretreatment yielded erratic results.

Colorimetric Determination of Cyclamate

A colorimetric method for the determination of cyclamate in foods, based on the reaction of cyclohexanol with vanillin-sulfuric acid reagent, was established. After separation of cyclamate from other components by dialysis pretreatment, cyclamate was converted to cyclohexyl nitrite with nitrous acid under cooling in an ice bath and then to cyclohexanol with sulfamic acid. Cyclohexanol was extracted with ether. After the addition of water to the extract, the ether was evaporated by vigorous stirring using a mixer at room temperature. Vanillin-sulfuric acid reagent was added little by little to the remaining water layer containing cyclohexanol under cooling in an ice bath and warmed for 20 minutes at 70°to form a greenish product. The colored solution was measured spectrophotometrically at 655 mμ. The recovery of sodium cyclamate added to some foods was 93.2-98.8%.