UASB Treatment of Tapioca Starch Wastewater

Feasibility of the upflow anaerobic sludge blanket (UASB) process was investigated for the treatment of tapioca starch industry wastewater. After removal of suspended solids by simple gravity settling, starch wastewater was used as a feed. Start-up of a 21.5-L reactor with diluted feed of approximately 3,000 mg∕L chemical oxygen demand (COD) was accomplished in about 6 weeks using seed sludge from an anaerobic pond treating tapioca starch wastewater. By the end of the start-up period, gas productivity of 4–5 m3/m3r?day was obtained. Undiluted supernatant wastewater with a COD concentration of 12,000–24,000 mg∕L was fed during steady-state reactor operation at an organic loading rate of 10–16 kg COD/m3r?day. The upflow velocity was maintained at 0.5 m∕h with a recirculation ratio of 4:1. COD conversion efficiencies >95% and gas productivity of 5–8 m3/m3r?day were obtained. These results indicated that removal of starch solids from wastewater by simple gravity settling was sufficient to obtain satisfactory performance of the UASB process.     

Acidification of Lactose in Wastewater

Acidification of lactose in wastewater was conducted in four series of experiments in an upflow reactor to investigate individual effects of hydraulic retention time (HRT) (2–24 h), lactose concentration in wastewater (2–30 g COD∕L), pH (4.0–6.5), and temperature (20°–60°C). Optimum acidification was found at pH 5.5 and 55°C. Acidification increased with HRT, but with the decrease of lactose concentration in wastewater. Degradation of lactose followed the Michaelis-Menten model with a maximum specific degradation rate of 4.39 g∕g VSS?day and a half-rate concentration of 1.97 g∕L. Production of volatile fatty acids, in general, favored lower lactose concentrations and higher pH, but was not sensitive to HRT and temperature. Distribution of individual volatile fatty acids∕alcohols was dependent on lactose concentration, pH, and temperature, but less sensitive to HRT. Under most conditions acetate, propionate, and ethanol were the predominant products. Biogas produced under all test conditions was composed of mostly hydrogen and carbon dioxide, but no detectable methane. Sludge yield was estimated as 0.230 ± 0.021 g VSS∕g COD.     

Effect of Carbon Source on PCE Dehalogenation

A laboratory study using the upflow anaerobic sludge blanket reactor for treating high-strength wastewater containing tetrachloroethene (PCE) was carried out to study the effect of carbon source, recycle, and shock loading on dehalogenation of PCE and process performance. The PCE was dehalogenated to trichloroethylene, cis-1,2-dichloroethylene, vinyl chloride, and ethylene. During the study on the effect of carbon source, the PCE and COD removal up to 97% and biogas production of 0.518–0.47 m3∕kg CODrem with methane content up to 66% were achieved under steady-state operating conditions. An increase in the influent COD from 2,000 to 4,000 mg∕L did not show any improvement in the PCE removal. Recycling of effluent at 50% showed the decrease in COD removal and increase in the effluent concentration of dichloroethylene and vinyl chlorides. Around 1–3.5% of influent PCE stripping to biogas was observed. It was observed that methanol has the stimulatory effect on the dehalogenation of PCE. A shock loading study showed that the upflow anaerobic sludge blanket reactor could assimilate 1.5–2 times the original PCE concentration (50 mg∕L) without much effect on the process performance.     

Rotating-Perforated-Tubes Biofilm Reactor for High-Strength Wastewater Treatment

A rotating-perforated-tubes biofilm reactor was used for treatment of synthetic wastewater at different operating conditions. The biofilm reactor consisted of two sections each having 25 perforated tubes mounted on three perforated discs. The battery of the tubes was rotated with the aid of a shaft and a motor. Effects of major process variables such as feed wastewater flow rate and COD concentration on the system performance were investigated. Kinetics of COD removal was investigated and kinetic constants determined by using the experimental data. An empirical design equation was developed to quantify the system's performance as a function of major process variables.     

Automatic Start-Up of UASB Reactors

A control system to automate the start-up of anaerobic wastewater treatment reactors is presented. The system controls the feedflow rate, using the biogas production or the biogas flow rate as the only on-line variable. Furthermore, other off-line parameters, such as methane content in the biogas and COD of influent are also necessary to calculate the COD balance in the reactor. Two different start-up strategies were applied: fed batch and continuous operation. In the fed-batch operation the frequency of feeding is automatically set depending on the efficiency in COD removal. The residual organic load fraction (the fraction of influent COD not degraded to methane), is the key parameter enabling the controller the modification of feeding frequency. In order to improve reliability of the system, a second parameter k representing the gas flow rate, was introduced. By using this strategy, starting from an organic loading rate (OLR) lower than 0.5 kg COD∕(m3?day), a load higher than 8 kg COD∕(m3?day) was achieved in only 33 days, with an efficiency, in terms of COD removal, higher than 90%. When the system was operated in continuous mode, the key parameter applied is again the residual organic loading rate fraction, expressed as the percentage of COD that remained undegraded in methane. Two extreme values—“minimum” and “maximum”—have to be defined. Once the system reaches the minimum, the controller increases the feeding pump speed automatically, and when it attains the maximum value, the feeding flow is decreased proportionally. In order to ensure stable operation, a further parameter, the waiting time between the moment at which the threshold value is reached and the modification of the feeding flow rate, was introduced. 24 h has proven to be an excellent value for this purpose. By means of this strategy, starting from an influent OLR lower than 0.5 kg COD∕(m3?day), an OLR of 9–12 kg COD∕(m3?day) was achieved in 40 days, with COD removal efficiency higher than 95%.     

电渗析处理钕铁硼废料回收稀土过程中高盐难降解废水

利用电渗析技术对钕铁硼废料回收稀土冶炼过程中产生的高盐难降解废水进行脱盐处理,研究了浓室与淡室体积比、操作电压、极水浓度、原料液与极水流量等对脱盐性能影响及废水COD变化情况。研究发现：利用电渗析技术,废水脱盐率可达93%以上,淡室中废水的COD得到降解,浓室中废水的COD基本不会富集,电耗为15.9 kWh/m3,为钕铁硼废料冶炼废水处理提供了技术支撑。     

Biotransformation of Carbon Tetrachloride and Anaerobic Granulation in a Upflow Anaerobic Sludge Blanket Reactor

Carbon tetrachloride (CT) in a synthetic wastewater was effectively degraded in a 2?l upflow anaerobic sludge blanket reactor during the granulation process by increasing the chemical oxygen demand (COD) and CT loadings. The effect of operational parameters such as influent CT concentrations, COD, CT loading, food to mass (F/M) ratio, and specific methanogenic activity (SMA) were also detected during granulation. Over 97% of CT was removed at 37°C, at a COD loading rate of 10?g/L?day. Chemical oxygen demand and CT removal efficiencies of 92 and 88% were achieved when the reactor was operating at CT and COD loading rates of 17.5?mg/L?day and 12.5?g/L?day, respectively. This corresponds to an hydraulic retention time of 0.28?day and an F/M ratio of 0.57?g?COD/g?volatile?suspended?solids?(VSS)?day. In 4?weeks, the seed sludge developed the CT degrading capability that was not very sensitive to shocks. The granular sludge cultivated had a maximum diameter of 2.5?mm and SMA of 1.64?g?COD/g?VSS?day. Glucose biodegradation by CT acclimated anaerobic granules was expressed with competitive inhibition. However the competitive inhibition was not significant since the competitive inhibition coefficient (Ki) was as high as 18.72?mg/L. Kinetic coefficients of k (maximum specific substrate utilization rate), Ks (half velocity coefficient), Y (growth yield coefficient), and b (decay coefficient) were determined as 0.6/day, 1.1?mg/L, 0.23?g?VSS/g glucose-COD, and 0.01/day, respectively, based on growth substrate glucose–COD during CT biotransformation. The CT was treated via biodegradation and this contributed to 89% of the total removal. The removal contributions from biomass adsorption, abiotic transformation, and volatilization were negligible. Adsorption and volatilization accounted for only 0.8 and 0.5% of the total removal, respectively.     

Treatment of Styrene-Contaminated Airstream in Biotrickling Filter Packed with Slags

This paper reports the result of studies using a biotrickling filter with blast-furnace slag packings (sizes = 2–4 cm and specific surface area = 120 m2∕m3) for treatment of styrene in an airstream. The effects of volumetric styrene loading L, superficial gas velocity U0 and liquid recirculation rate VL on the styrene elimination capacity K, and the removal efficiency K∕L were tested. Variations of styrene concentration with packing height as well as rates of nutrient utilization were also tested. The results show that for L< 30 g∕m3?h, K∕L was nearly independent of U0 in the range of 29–67 m∕h and was independent of VL in the range of 3.84–9.60 m∕h. In this range, the rate of styrene removal was both reaction and diffusion limited and the reaction was of zero-order kinetics. For higher loadings, K∕L decreased with increasing U0 and increased with increasing VL and the system approached the condition of reaction limitation.     

2,4,6 Tri-Chlorophenol Containing Wastewater Treatment Using a Hybrid-Loop Bioreactor System

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with an effluent recycle was used for biological treatment of 2,4,6 tri-chlorophenol (TCP) containing synthetic wastewater. The effects of sludge age (solids retention time) on chemical oxygen demand (COD), TCP, and toxicity removal performance of the system were investigated for sludge ages between 5 and 30?days, while the feed COD (2600±100?mg?L?1), TCP (370±10?mg?L?1), and the hydraulic residence time (25?h) were constant. Percent TCP, COD, and toxicity removals increased with increasing sludge age resulting in nearly complete COD, TCP, and toxicity removal at sludge ages above 20?days. Biomass concentrations in the packed column and in the aeration tank increased with increasing sludge age resulting in low reactor TCP concentrations, and therefore, high TCP, COD, and toxicity removals. More than 95% of COD, TCP, and toxicity removal took place in the packed column reactor. Volumetric rates of TCP and COD removal increased due to increasing biomass and decreasing effluent TCP and COD concentrations with increasing sludge age. The specific rate of TCP removal was maximum (120?mg?TCP?gX?1?day?1) at a sludge age of 20?days. TCP inhibition was eliminated by operation of the system at sludge age above 20?days to obtain nearly complete COD, TCP, and toxicity removal.     

Influence of COD:N:P Ratio on Nitrogen and Phosphorus Removal in Fixed-Bed Filter

This study examined the effects of COD:N:P ratio on nitrogen and phosphorus removal in a single upflow fixed-bed filter provided with anaerobic, anoxic, and aerobic conditions through effluent and sludge recirculation and diffused air aeration. A high-strength wastewater mainly made of peptone, ammonium chloride, monopotassium phosphate, and sodium bicarbonate with varying COD, N, and P concentrations (COD: 2,500–6,000, N: 25–100, and P: 20–50 mg/L) was used as a substrate feed. Sodium acetate provided about 1,500 mg/L of the wastewater COD while the remainder was provided by glucose and peptone. A series of orthogonal tests using three factors, namely, COD, N, and P concentrations, at three different concentration levels were carried out. The experimental results obtained revealed that phosphorus removal efficiency was affected more by its own concentration than that of COD and N concentrations; while nitrogen removal efficiency was unaffected by different phosphorus concentrations. At a COD:N:P ratio of 300:5:1, both nitrogen and phosphorus were effectively removed using the filter, with removal efficiencies at 87 and 76%, respectively, under volumetric loadings of 0.1?kg?N/m3?d and 0.02?kg?P/m3?d.     

Removal of Heavy Metals and COD by SRB in UAFF Reactor

Sulfate-reducing bacteria, under anaerobic conditions, reduce sulfate, SO4?2, to sulfide, S?2, which in turn can effectively precipitate heavy metals. In this research project, sulfate-reducing bacteria were grown in an upflow anaerobic fixed-film (UAFF) reactor using optimum growth conditions obtained in previous studies. These reactors were then fed with different heavy metals at increasing loading rates until complete failure occurred as metal removal reached zero and residual sulfide dropped to zero. The metal concentrations were measured as total, dissolved, and free ions both in the influent and in the effluent streams. The results of this research showed that 100% removal efficiencies could be obtained with individual concentrations up to 200 mg∕L for Cu, 150 mg∕L for Ni and Zn, 75 mg∕L for Cr, 50 mg∕L for Cd, and 40 mg∕L for Pb. Also, the corresponding organic matter removal as total organic carbon was found to be about 50% of the influent total organic carbon. A set of mathematical equations were derived to express the mass balance inside the UAFF reactor, with respect to metal influent concentrations and sulfide production. These equations were corrected by incorporating a correction product, α?β, to represent the toxicity effect of the increasing metal concentrations.     

Organic Removal of Anaerobically Treated Leachate by Fenton Coagulation

The leachate from a Hong Kong landfill, containing 15,700 mg∕L of chemical oxygen demand (COD) and 2,260 mg∕L of ammonia nitrogen (NH3–N), was first treated in a UASB (upflow anaerobic sludge blanket) reactor at 37°C. The process on average removed 90.4% of COD with 6.6 days of hydraulic retention at an organic loading rate of 2.37 g of COD∕L?day. The UASB effluent was further treated by the Fenton coagulation process using H2O2 and Fe2+. Under the optimal condition of 200 mg of H2O2∕L and 300 mg of Fe2+∕L and an initial pH of 6.0, 70% of residual COD in the UASB effluent was removed, of which 56% was removed by coagulation∕precipitation and only 14% by free radical oxidation. It is obvious that H2O2 and Fe2+ had a strong synergistic effect on coagulation. The average COD in the final effluent was 447 mg∕L. Removing each gram of COD required 0.28 g of Fe2+ and 0.18 g of H2O2.     

Biodegradation of Phenol with Wastewater as a Cosubstrate in Upflow Anaerobic Sludge Blanket

Anaerobic degradation of phenol mixed with a readily degradable synthetic wastewater (DSWW) as a cosubstrate was studied in a 12?L upflow anaerobic sludge blanket reactor at 30±2°C over a period of 632?days. DSWW was prepared by diluting sugar cane based molasses. The biomass was acclimatized to high phenol concentration by gradually decreasing the DSWW chemical oxygen demand (COD) of 4,000?mg/L. Feed made up of phenol COD and DSWW COD in the ratio of 7:3 (phenol concentration = 1,176?mg/L) was successfully treated at a hydraulic retention time (HRT) of 12?h and organic loading rate (OLR) of 8?g?COD/L?day. Phenol removal ranged from 99.9 to 84% at phenol COD varying from 10 to 70% in the feed. During the entire operation, COD removal varied from about 74 to 91.3%. The influent COD was distributed into CH4–COD ( ～ 72%), effluent COD ( ～ 17%), and sludge and unaccounted COD ( ～ 11%). The process failure occurred at 4:1 phenol COD: DSWW COD. Specific methanogenic activity of granular sludge exhibited uniform activity up to phenol COD of 70%. The performance of the reactor could not be maintained beyond 70% phenol COD even by reducing the sludge loading rate, increasing HRT, or decreasing OLR.     

Treatment and Decolorization of Dyes in an Anaerobic Baffled Reactor

Synthetic organic colorants, the majority of which are recalcitrant in nature, are used universally in many different manufacturing processes. The dyes are released into the environment in industrial effluents and are highly visible even at low concentrations (<1 mg∕L). Added to this, certain dyes, dye precursors, and aromatic amines have been shown to be carcinogenic. Thus, appropriate treatment of dye wastewaters to remove color and the dye compounds is clearly an important issue. Methanogenic toxicity tests on several food dyes provided a range of toxicity results, from noninhibitory (IC50 >20 g∕L) to inhibitory (IC50 0.2 mg∕L). Batch biodegradability assays indicated that the dyes were not readily utilized by the anaerobic microorganisms as a sole substrate. Decolorization of the dye tartrazine was investigated in a laboratory-scale anaerobic baffled reactor at a concentration of 250 mg∕L. Reduction in COD of 50–60% and color reduction of about 95% was achieved. Initially the tartrazine was not readily decolorized; however, decolorization improved with acclimation of the biomass. An industrial wastewater from a food dye manufacturer was fed to a second laboratory-scale anaerobic baffled reactor at a concentration of 5% (volume-to-volume ratio) and then increased to 10% (volume-to-volume ratio). Anaerobic degradation of the wastewater was efficient. Methanogenic activity was high; the organic content of the influent was reduced by about 70%, and color was reduced by almost 90%     

Use of Sequencing Batch Reactor for Biological Denitrification of High Nitrate-Containing Water

The efficiency of a sequencing batch reactor in denitrification of drinking water with relatively high nitrate concentrations (40–250 mg∕L as N) was evaluated. Ethanol at a COD∕N of 2.00 was found sufficient to reduce nitrate concentrations to acceptable levels (<10 mg∕L as N). Within the first 6 min of reaction, nitrite accumulation in the range of 0.03–3.5 mg∕L as N was observed increasing with the increase of initial nitrate concentrations. In the first hour, nitrate removal was significantly high in the range of 85.7–91.5%. Anoxic reaction times of 3, 5, and 7 h were required for nitrate concentrations of 40–160, 200, and 250 mg∕L (as N) to achieve acceptable levels of nitrate and nitrite. Alkalinity of the denitrified water increased on average by 3.53 mg as CaCO3 for each milligram of nitrate reduced and pH increased from 7.3 to the range of 8 to 9. Idle times between the operation cycles, in the range of 1–14 h, had an insignificant effect on denitrification. Residual COD concentrations in the range of 5–15 mg∕L and sulfide concentrations (at initial nitrate concentrations ≥120 mg∕L as N) in the range of 0.2–0.4 mg∕L were recorded in the finished water. Elevated concentrations of COD in general are not advisable in drinking water, and specifically in this case, it could result in toxic sulfide formation in the treated water. There is a need to further study the optimization of the use of ethanol and polishing of the treated water. A sequencing batch reactor has the potential of being used as an alternative configuration for biological denitrification of drinking water.     

Metal Bioavailability and Trivalent Chromium Removal in ABR

Trace metal bioavailability and chromium(III) removal were investigated in an anaerobic baffled reactor (ABR) treating a synthetic waste [COD = 4,000 mg∕L, COD:SO42? ratio 8:1 and 40:1, Cr(III) = 50 mg∕L]. Sulfide precipitation reduced nutrient bioavailability as follows (most deficient first): Fe > Co > Ni. However, the metals had the following affinity for complexation: Ni > Co >> Fe; complexation potential was greatest at the front and rear of the reactor. At the front, it was hypothesized that high concentrations of soluble microbial products provided an excess of potential ligands, which may have sequestered the metals. However, in the last compartment, a higher pH would have altered the competition between protons and metal cations for complexing sites in favor of the metal cations. The complexing potential in the ABR increased with sulfide levels, and this coincided with higher residual COD production, probably to provide a diffusion barrier to the harsh environmental conditions. Although the addition of chromium (50 mg∕L) had no observable effect on reactor performance∕stability, its removal was controlled by the following factors (most influential first): solubility > complexation > absorption > physical adsorption.     

Preparation and application of pharmaceutical wastewater treatment by praseodymium doped SnO2/Ti electrocatalytic electrode

Praseodymium was selected as a promoter for SnO2/Ti electrode to improve the electrocatalytic performance by electrodeposition in pharmaceutical wastewater treatment; the micrograph and the structure were characterized by SEM and XRD. Mixture uniform design was used in the optimization of the electrolytic conditions; mathematical model was established according to the rate of wiping COD off, which revealed the relationship between the current intensity, time of electrolysis, the amount of doped Pr, and the ratio of area （SnOJTi：Al）. On the basis of the analysis of the empirical model, the optimized parameters had been obtained; the rate of wiping COD off was up to 94.9%, it decreased from 392 to 20 mg/L. Experimental results showed that the electrocatalytic performance of the electrode doped with Pr was superior for the treatment of pharmaceutical wastewater.     

Stress-Corrosion Cracking of AISI 4340 Steel in Aqueous Environments

Stress corrosion cracking of the high-strength martensitic steel AISI 4340 (yield stress = 1503 MPa) in NaCl aqueous solutions of different concentrations was studied experimentally using compact tension specimens in free corroding conditions. The experiments were conducted under the controls of constant load, constant crack opening displacement (COD), constant loading rate, and constant COD rate. Despite the differences in controlling conditions, the experiments yielded similar results for the threshold stress intensity factor and the plateau velocity in the 3.5 wt pct NaCl solution. Dependence of the plateau velocity on the NaCl concentration was observed, whereas the values of the threshold stress intensity factors seem to be independent of the NaCl concentration in distilled water.     

Investigation of Bond between Fiber Reinforced Polymer and Concrete Undergoing Global Mixed Mode I∕II Loading

A novel experimental method using modified double cantilever beam specimens and a customized test frame are introduced to evaluate bond characteristics and toughness of fiber reinforced polymer (FRP) composite overlays and a concrete substrate under mixed mode loading. A computer vision system is used to measure the crack location, near-tip deformations and crack opening displacement during the crack growth process. Digital image correlation is used to determine the crack opening displacement (COD) for flaws growing in the vicinity of the FRP–concrete interface. Results from this study indicate that during crack growth, (1) the Mode I component of COD is dominant for all angles of specimen loading, (2), the magnitude of the local Mode I component of COD is maximized when good bond quality is present and crack extension occurs within the mortar∕concrete near the FRP–concrete interface and (3) good agreement exists between independent energy release rate estimates based upon both an approximate elastic double cantilever beam formulation and also use of the measured components of COD in a classical linear elastic expression.