Percent Chemical Oxygen Demand Research Articles

Simultaneous removal of C, N, P from cheese whey by jet loop membrane bioreactor (JLMBR)

The membrane bioreactor (MBR) used in this study consisted of a jet loop bioreactor (aerobic high rate system) and a membrane separation unit (microfiltration). Jet loop membrane bioreactor (JLMBR) system is a high performance treatment system. High organic loading rates can be achieved with a very small footprint. The JLMBR is a compact biological treatment system which requires much smaller tank volumes than conventional activated sludge system. Solid–liquid separation is performed with a membrane. The JLMBR system, of 35 L capacity, was operated continuously for 3 months with a sludge age of 1.1–2.8 days and chemical oxygen demand (COD) loads of 3.5–33.5 kg COD m −3 day −1. The mean concentration values of COD, total nitrogen (TN) and PO 4 3− in cheese whey (CW) were found as 78,680 mg L −1, 1125 mg L −1 and 378 mg L −1, respectively. Ninety-seven percent COD removal rate was obtained at the sludge age ( Θ c) of 1.6 days and volumetric loads of 22.2 kg COD m −3 day −1. TN removal was obtained as 99% at the loading rates of 17–436 g TN m −3 day −1. PO 4 3− removals were between 65 and 88% for the loading of 30–134 g PO 4 3− m −3 day −1. The system could simultaneously remove the COD, TN and PO 4 3− at high efficiencies. The sludge flocks were highly motile, dispersed and had poor settling properties.

Hydraulic Residence Time Effects on Performance of an Activated Sludge Unit Treating Wastewater Containing Dichlorophenol

Wastewaters containing chlorophenol compounds are difficult to treat by biological means because of the toxic effects of those compounds on microorganisms. To investigate the adverse effects of chlorophenols on microorganisms, synthetic wastewater containing 2,4 dichlorophenol (DCP) was biologically treated in an activated sludge unit at different hydraulic residence times (HRTs) between 5 and 40 hours, whereas the feed chemical oxygen demand (COD), DCP concentrations, and sludge age were kept constant at 2500 +/- 50 mg/L, 150 mg/L, and 20 days, respectively. The resazurin method based on dehydrogenase activity was used for assessment of the feed and effluent wastewater toxicity. Percent COD, DCP, and toxicity removals increased, and the effluent COD, DCP, and toxicity levels decreased with increasing HRT. Biomass concentration in the aeration tank increased with increasing HRT because of low levels of DCP at high HRT levels, resulting in high COD, DCP, and toxicity removals. The sludge volume index decreased with increasing HRT, yielding well-settling organisms as a result of low levels of toxicity and high concentrations of active cells. Percent DCP and COD removals decreased with increasing specific DCP loading rate. The rates of DCP and COD removals showed a maximum at a low DCP concentration of 6 mg/L in the aeration tank, corresponding to a 25-hour HRT.

Removal of 2,4-dichlorophenol and toxicity from synthetic wastewater in a rotating perforated tube biofilm reactor

Chlorinated aromatic compounds present in many industrial effluents are usually removed by a combination of physical and chemical processes. Biological oxidation of chlorophenol compounds is difficult because of toxic effects of those compounds on microorganisms. A newly developed rotating perforated tubes biofilm reactor (RTBR) was used in continuous mode for removal of 2,4-dichlorophenol (DCP) and toxicity from synthetic wastewater. A special culture of Pseudomonas putida capable of degrading DCP supplemented activated sludge culture was used for this purpose. A Box–Wilson statistical experiment design method was used to investigate the effects of major operating parameters such as A/ Q ratio, feed chemical oxygen demand (COD) and feed 2,4-dichlorophenol concentrations on COD, DCP and toxicity removals. Experimental data were used for determination of the response function coefficients. Percent COD, DCP and toxicity removals determined from the response functions were in good agreement with the experimental data. A Resazurin method based on dehydrogenase activity was used for assessment of the toxicity for the feed and effluent wastewater. Low feed COD and DCP contents and high A/ Q ratios were found to be favorable for effective removal of DCP, COD and toxicity. Maximum percent DCP removal (nearly 100%) was obtained with a feed DCP concentration of 50 mg l −1, A/ Q ratio of 200 m 2 d m −3 and a feed COD of 2000 mg l −1, which resulted in COD and toxicity removal efficiencies of 96 and 79%, respectively.

Adsorbent supplemented biological treatment of pre-treated landfill leachate by fed-batch operation

Biological treatment of landfill leachate usually results in low COD removals because of high chemical oxygen demand (COD), high ammonium-N content and presence of toxic compounds. Coagulation–flocculation with lime addition and air stripping of ammonia were used as pre-treatment in this study in order to improve biological treatability of the leachate. Pre-treated leachate was subjected to adsorbent supplemented biological treatment in an aeration tank operated in fed-batch mode. COD and NH 4-N removal performances of powdered activated carbon (PAC) and powdered zeolite (PZ) were compared during biological treatment. Adsorbent concentrations varied between 0 and 5 g l −1. Percent COD and ammonium-N removals increased with increasing adsorbent concentrations. Percent COD removals with PAC addition were significantly higher than those obtained with the zeolite. However, zeolite performed better than the PAC in ammonium-N removal from the leachate. Nearly 87% and 77% COD removals were achieved with PAC and zeolite concentrations of 2 g l −1, respectively. Ammonium-N removals were 30% and 40% with PAC and zeolite concentrations of 5 g l −1, respectively at the end of 30 h of fed-batch operation.

Repeated fed-batch biological treatment of pre-treated landfill leachate by powdered activated carbon addition

High chemical oxygen demand (COD), high ammonium-N content and presence of toxic compounds such as heavy metals result in low removal efficiencies in direct biological treatment of landfill leachate. Raw landfill leachate was subjected to pre-treatment by coagulation-flocculation and air stripping of ammonia before biological treatment. Pre-treated leachate was subjected to biological treatment in an aeration tank operated in repeated fed-batch mode in the absence and presence of powdered activated carbon (PAC) as adsorbent. Three different cycles of 1×30 h, 3×10 h, and 5×6 h were used in the absence and presence of 2 g l −1 PAC. The results clearly indicated that PAC addition has improved COD removal significantly as compared to PAC-free biological treatment. Repeated fed-batch treatment also resulted in lower effluent COD and higher COD removal efficiencies as compared to single-cycle operation. The feed COD of 7000 mg l −1 was reduced to final COD values of 365 mg l −1 and 875 mg l −1 in repeated fed-batch experiments with 5×6 h cycles in the presence (2 g l −1 PAC) and absence of PAC, respectively. Repeated fed-batch operation with 3×30 h cycle length resulted in percent COD removal and final COD content of 94% and 285 mg l −1, respectively, with 2 g l −1 PAC addition.

Anaerobic hydrolysis of a municipal wastewater in a pilot-scale digester

Raw domestic wastewater from the city of Santiago de Compostela (Northwest Spain) was fed into a pilot-scale hydrolytic up flow sludge bed (HUSB) digester with an active volume of 25.5 m3. The total influent chemical oxygen demand (COD) ranged from 360 to 470 mg/l, the influent SS varied from 190 to 370 mg/l, and the temperature was between 17 degrees and 20 degrees C. The organic load rate (OLR) applied increased step by step from 1.2 to 3.9 kgCOD/m3 x d, while the hydraulic retention time (HRT) decreased from 7.1 h to 2.9 h. A high suspended solids (SS) removal of about 82-85% from the influent was reached, most of which (81 to 88%) was eliminated by hydrolysis, while the rest remained in the purge stream. The total COD removal ranged from 46 to 59%. On the other hand, a high acidification of the COD remaining in the effluent was obtained, so the percent COD in the form of volatile fatty acids (VFA(COD)) with respect to total effluent COD was about 43% for the highest HRT applied, and about 27% for the lowest HRT. The soluble to total COD ratio (CODs/CODt) increased from 25-32% for the influent to 71-86% for the effluent. The results obtained confirm the viability and interest of direct anaerobic hydrolytic pre-treatment of domestic wastewater.

Effects of 2,4-dichlorophenol on activated sludge.

The effects of 2,4-dichlorophenol (2,4-DCP) on both acclimated and unacclimated activated sludge were investigated in batch reactors. The IC(50) values on the basis of maximum specific growth rate ( micro(m)), percent chemical oxygen demand (COD) removal efficiency and sludge activity were found to be 72, 60 and 47 mg l(-1), respectively, for unacclimated culture. The percent COD removal efficiencies of unacclimated culture were affected adversely, even at low concentrations, whereas culture acclimated to 75 mg 2,4-DCP l(-1) could tolerate about 200 mg 2,4-DCP l(-1)on the basis of COD removal efficiency. Although yield coefficient values of unacclimated culture increased surprisingly to very high values with the addition of 2,4-DCP, a linear decrease with respect to 2,4-DCP concentrations was observed for acclimated culture. Although no removal was observed with unacclimated culture, almost complete removal of 2,4-DCP up to a concentration of 148.7 mg l(-1) was observed with acclimated culture. It was showed that the culture could use 2,4-DCP as sole organic carbon source, although higher removal efficiencies in the presence of a readily degradable substrate were observed. Culture acclimated to 4-chlorophenol used 2,4-DCP as sole organic carbon source better than those acclimated to 2,4-DCP.

Aerobic biotreatment of wastewater from dimethyl terephthalate plant using biomass support particles

Biotreatment of wastewater from a dimethyl terephthalate (DMT) plant in repeated batch mode with 24-h cycles and feed chemical oxygen demand (COD) of 2000 mg/ l, led to a COD reduction of approximately 86% in 20 h. Incorporation of porous plastic biomass support particles (BSP) in the reactor however, resulted in similar COD reduction in only 6 h. The increased percentage COD reduction in BSP reactor was found to be related to the increase in biomass (from 2.8 to 10.5 g/ l) in the reactor. In the continuous mode, the optimum organic loading and hydraulic retention time (HRT) for more than 90% COD reduction were found to be approximately 14 kg COD/m 3/d and 12 h, respectively, with the BSP reactor. On the other hand, only 40–45% COD reduction was observed under the same conditions in the reactor not containing the support particles. Reduction in percentage COD reduction at high organic loading rates was due to the presence of formaldehyde in the wastewater feed. The control reactor, not containing BSP, was found to be sensitive to formaldehyde concentrations above 160 mg/ l, while the reactor with BSP was resistant up to a formaldehyde concentration of 410 mg/ l. The advantages of the BSP augmentation for the aerobic biotreatment of DMT wastewater are discussed.

A Novel Method for Biological Treatment of Bleached Kraft Mill Wastewaters

Removal of adsorbable organic halogen (AOX) and chemical oxygen demand (COD) from bleached kraft mill effluent was investigated in laboratory and pilot scale aerobic suspended carrier reactors and abiotic thermo-alkaline reactors. Laboratory treatment focused on determination of loading capacity of the suspended carrier process and operation of the process at elevated temperature and pH values in order to combine abiotic thermo-alkaline dechlorination and biological treatment in one reactor. At pH 7, 37°C and hydraulic retention times (HRTs) longer than 3.5 hours, a maximum COD removal of 55% was achieved in the suspended carrier process. The COD conversion rate at the minimum HRT was 2.6 kg COD/(m3*d). The suspended carrier treatment was operated successfully at pH 9.0 and 45°C and at pH 7.0 and 50°C with over 50 percent COD removal with a HRT of four hours. The AOX removal achieved at pH 9 and 45°C (50%) was significantly higher than the removal at pH 7 and 37°C (39%), most certainly because of an increased abiotic dechlorination at the higher pH and temperature levels. Sequential thermo-alkaline and biological treatment were studied on a pilot scale. Tbermo-alkaline treatment at pH 10, 54°C and a HRT of two hours followed by biological treatment at pH 8, 35°C and a HRT of four hours, removed almost 80% of AOX and 50% of COD from the kraft mill effluent.

Carbon-to-Nitrogen Ratio and Hydraulic Retention Time Effect on the Anaerobic Digestion of Cheese Whey

ABSTRACT SIXTEEN 1-L digesters were used to test four carbon-to-nitrogen ratios of 8.4, 13.9, 22.2 and 27.6 and four hydraulic retention times of 12, 18, 24 and 30 days on the efficiency of digester operation. Percent methane in the biogas and methane production were dependent on both carbon-to-nitrogen ratio and hydraulic retention times. Percent chemical oxygen demand reduction, volatile solids removal, total volatile acids concentrations, digester pH and amount of sodium hydroxide solution needed to control digester pH were dependent on hydraulic retention time only.