Chemical oxygen demand reduction in coffee wastewater through chemical flocculation and advanced oxidation processes

The removal of the natural organic matter present in coffee processing wastewater through chemical coagulation-flocculation and advanced oxidation processes （AOP） had been studied. The effectiveness of the removal of natural organic matter using commercial flocculants and UV/H202, UV/O3 and UV/H2O2/O3 processes was determined under acidic conditions. For each of these processes, different operational conditions were explored to optimize the treatment efficiency of the coffee wastewater. Coffee wastewater is characterized by a high chemical oxygen demand （COD） and low total suspended solids. The outcomes of coffee wastewater treatment using coagulation-flocculation and photodegradation processes were assessed in terms of reduction of COD, color, and turbidity. It was found that a reduction in COD of 67% could be realized when the coffee wastewater was treated by chemical coagulation-flocculation with lime and coagulant T-1. When coffee wastewater was treated by coagulation-flocculation in combination with UV/H2O2, a COD reduction of 86% was achieved, although only after prolonged UV irradiation. Of the three advanced oxidation processes considered, UV/H2O2, UV/O3 and UV/H2O2/O3, we found that the treatment with UV/H2O2/O3 was the most effective, with an efficiency of color, turbidity and further COD removal of 87%, when applied to the flocculated coffee wastewater.

Simultaneous Determination of Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD5) in Wastewater by Near-Infrared Spectrometry

To rapidly determine the pollution extent of wastewater, the calibration models were established for deter-mination of Chemical Oxygen Demand and Biological Oxygen Demand in wastewater by partial least squares and near infrared spectrometry of 120 samples. Spectral data preprocessing and outliers’ diagnosis were also discussed. Correlation coefficients of the models were 0.9542 and 0.9652, and the root mean square error of prediction (RMSEP) were 25.24 mg?L-1 and 12.13 mg?L-1 in the predicted range of 28.40~528.0 mg?L-1 and 16.0~305.2 mg?L-1 for Chemical Oxygen Demand and Biological Oxygen Demand, respectively. By statistical significance test, the results of determination were compared with those of stan-dard methods with no significant difference at 0.05 level. The method has been applied to simultaneous de-termination of Chemical Oxygen Demand and Biological Oxygen Demand in wastewater with satisfactory results.

Environmental capacity of chemical oxygen demand in the Bohai Sea: modeling and calculation

A three-dimensional advection-diffusion model coupled with the degradation process is established for describing the transport of chemical oxygen demand (COD). Comparison of the simulated distribution of COD at the surface in the Bohai Sea in August, 2001 with field observations, shows that the model simulates the dataset reasonably well. The Laizhou Bay, Bohai Bay, and Liaodong Bay were contaminated heavily near shore. Based on the optimal discharge flux method, the Environmental Capacity (EC) and allocated capacities of COD in the Bohai Sea are calculated. For seawater of Grades I to IV of the Chinese National Standard, the ECs of COD in the Bohai Sea were 77×104 t/a, 116×104 t/a, 154×104 t/a and 193×104 t/a, respectively. The Huanghe (Yellow) River pollutant discharge accounted for the largest percentage of COD at 14.3%, followed by that of from the Liugu River (11.5%), and other nine local rivers below 10%. The COD level in 2005 was worse than that of Grade II seawater and was beyond the environmental capacity. In average, 35% COD reduction is called to meet the standard of Grade I seawater.

Spatial distribution and diurnal variation of chemical oxygen demand at the beginning of the rainy season in the Changjiang (Yangtze) River Estuary

A field observation was carried out in the Changjiang (Yangtze) River Estuary from May 19 to 26, 2003. A total of 29 stations, including 2 anchored stations, were occupied through almost the whole salinity gradient. Based on the observation data, biogeochemistry of chemical oxygen demand (COD) was examined. Spatial distribution pattern of COD shows that it decreased downstream. The COD concentration varied generally within a narrow range of 1.24–1.60 mg/L in the zone around the river mouth, beyond which it decreased rapidly to 0.20 mg/L. In the mixed water zone, the fluctuation in COD was smaller at 2 m above the bottom layer than at the surface layer in 48 h. In the seawater zone, the 48-h fluctuation at the surface was the largest, followed by that of 5 m below the surface and 2 m above the bottom layers in a range of from 2.50 to 0.55 mg/L. Freshwater discharge was the dominant source of COD in the estuary. The average COD beyond the river mouth was 2.7 mg/L, which accorded with the Chinese seawater quality Grade I. Relationships between dissolved oxygen and biogeochemical parameters such as suspended particulate matter, dissolved organic matter and chlorophyll-a were also discussed.

On-Line Measurement of the Chemical Oxygen Demand in Wastewater in a Pulp and Paper Mill Using Near Infrared Spectroscopy

Although near infrared (NIR) spectroscopy has been evaluated for numerous applications, the number of actual on-line or even on-site industrial applications seems to be very limited. In the present paper, the attempts to produce online predictions of the chemical oxygen demand (COD) in wastewater from a pulp and paper mill using NIR spectroscopy are described. The task was perceived as very challenging, but with a root mean square error of prediction of 149 mg/l, roughly corresponding to 1/10 of the studied concentration interval, this attempt was deemed as successful. This result was obtained by using partial least squares model regression, interpolated reference values for calibration purposes, and by evenly distributing the calibration data in the concentration space. This work may also represent the first industrial application of online COD measurements in wastewater using NIR spectroscopy.

Electrochemical Degradation of Indigocarmine Dye at Ni/Graphite Modified Electrode in Aqueous Solution

Nickel Graphite modified electrode (Ni/GME) was prepared by electrochemical method and degradation of Indigocarmine (IC) dye was carried out. An investigation between the efficiency of degradation by graphite electrode and the Ni/graphite modified electrode has been carried out. The different effects of concentration, current density and temperature on the rate of degradation were studied. This study shows that the rate of the degradation is more for Ni doped modified graphite electrode. UV-Visible spectra before and after degradation of the dye solution were observed. The thin film formation of Ni or encapsulated in graphite rod is observed by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM & EDAX). The instantaneous current effectiveness values of different experimental conditions are evaluated. The anodic oxidation by Ni/ graphite modified electrode showed the complete degradation of aqueous solution indigocarmine, which is confirmed by UV-Visible and chemical oxygen demand (COD) measurements. The dye is converted into CO2, H2O and simpler inorganic salts. The results observed for reuse of modified electrodes indicate that the Ni/graphite modified electrode would be a promising anode for electrochemical degradation of indigocarmine. This method can be applied for the remediation of waste water containing organics, cost-effective and simple.

Characterization and analysis of petrochemical wastewater through particle size distribution, biodegradability, and chemical composition

The centralized treatment method is a widely used form of wastewater treatment that tends to be less effective at removing toxic substances. Therefore, a detailed analysis of the composition of wastewater can provide important information for the design of an effective wastewater treatment process. The objective of this paper was to investigate particle size distribution(PSD), biodegradability, and the chemical composition of the petrochemical wastewater discharges. For this purpose, this project selected the petrochemical wastewater and treated wastewater of China National Offshore Oil Corporation Zhongjie Petrochemical Co, Ltd. as the analysis objects.The step-by-step filtration method, along with a molecular weight classification method, was selected to build the chemical oxygen demand(COD) and biochemical oxygen demand(BOD) fingerprints of petrochemical wastewater and treated wastewater. The results showed that the main pollutants were settleable particles in petrochemical wastewater, which contributed to over 54.85% of the total COD. The colloidal particles with particle sizes in the range of 450–1000 nm had the highest COD value in the treated wastewater, which contributed34.17% of the total COD of treated wastewater. The results of the BOD analysis showed that the soluble fractions were the main reason that treated wastewaters did not meet the treatment standards. Tests on the organic compounds in petrochemical wastewater found that there were mainly linear paraffins, branched paraffins, benzene series compounds, and some plasticizers in the influent of the petrochemical wastewater. The most abundant pollutants in treated petrochemical wastewater were the adjacent diisobutyl phthalate and the linear alkanes.Fourier transform infrared(FTIR) transmission spectroscopy analysis showed that the settleable particles of petrochemical wastewater and membrane bioreactor(MBR)-treated wastewater contained multiple types of organic substances. The results also indicated that removing the oil-settleable substances, the colloidal particles(450–1000 nm), and the soluble organics will be necessary for the treatment of petrochemical wastewater.

Disruption of biofilms from sewage pipes under physical and chemical conditioning

Biofilms grown inside two sewage collecting pipes located in industrial and residential areas are studied. Bacterial biomass inside three layers of biofilms was evaluated. Biofilm cohesion under different mixing rate and ionic strength was also investigated. Effects of physical and chemical parameters in the biofilms were evaluated by monitoring turbidity, chemical and biochemical oxygen demands. Extracted organic matter from biofilms was partitioned to polar, aromatic and saturated fractions using activated silica column chromatography. Results revealed that bacterial biomass growth depending on biofilm thickness and stratification. The most loaded stratum in bacteria/biomass was the sewage-biofilm interface stratum that represented 51% of the total bacteria/biomass. Stirring rate and ionic strength of mono- and bivalent salts showed a major influence in biofilm disruption. The stirring time enhanced the exchange dynamic and matter capture between biofilm fragments at the critical stirring rate 90 r/min. Sodium chloride showed the dispersing effect on biofilms in suspension, and decreased the BOD5 （biochemical oxygen demand） beyond the physiological salt concentration.

Effects of Urechis unicinctus Juveniles on Chemical Characteristics of Organically Contaminated Coastal Sediment

Biological activities of marine benthos such as burrowing and feeding may change sediment characteristics.We conducted three experiments to examine the potential of using juveniles of a spoon worm Urechis unicinctus to improve the quality of organically contaminated coastal sediment.Sediment samples were collected from a site that was heavily contaminated with organic matter (Seonso) and two sites that were clean (Myo-do,Dolsan-do).Urechis juveniles,obtained by artificial fertilization and cultured in the laboratory,were introduced to the sediment (weight 3 kg,depth 10 cm) at a density of 500 individuals per aquarium (length 50 cm,width 35 cm,height 30 cm) (Experiment 1),or at densities ranging from 100 to 900 individuals per beaker (Experiment 2).To examine how sediment contamination can be modified by the effects of Urechis,500 individuals (per aquarium) were exposed to the Seonso contaminated sediment that had been mixed with 0-100% clean sand (Experiment 3).Each experiment lasted two months and sediment samples were collected every 15 d to determine the several indexes of sediment quality,which included acid volatile sulfide (AVS),chemical oxygen demand (COD) and total ignition loss (TIL).In Experiment 1,the existence of Urechis did not result in significant changes in quality indexes in the sediments collected from Myo-do,Dolsan-do.However,AVS,COD and TIL of the Seonso sediment all decreased significantly after co-incubation with Urechis juveniles for 30 to 45 d.Experiment 2 showed that a density of at least 300 juveniles per beaker was necessary to significantly reduce all three quality indexes,and the magnitude of reduction was positively correlated with juvenile density.Experiment 3 revealed that Urechis juveniles were effective in reducing the AVS,COD and TIL of the Seonso sediment that had been mixed with 60%,80%,and 80% of clean sand,respectively.The results of the present study therefore indicated that juveniles of this spoon worm have the potential to be used to improve the quality of organically contaminated sediment in coastal waters.

Assessment of the Physicochemical and Microbiological Parameters of a Teaching Hospital’s Wastewaters in Abidjan in Côte d’Ivoire

This work deals with the physicochemical and microbiological characterization of a hospital wastewater that is directly discharged in water bodies without treatment. Our focus was paid on the teaching hospital of Treichville (Cote d’Ivoire). For the purpose, various physicochemical parameters such as temperature, pH, dissolved oxygen, total dissolved solid, conductivity, nitrate, phosphate, chloride, chemical oxygen demand (COD), biological oxygen demand for five days (BOD5), salinity, and total suspended solids have been assessed. For the microbiological investigations, the parameters consisting in Pseudomonas aeruginosa, Salmonella and total coliforms have been assessed. From the analysis, it has been found that the wastewaters of the teaching hospital of Treichville are highly loaded in organic pollutants and in pathogens bacteria. The values of nitrate, dissolved oxygen demand, COD, BOD5 and biological parameters do not respect the international (WHO) values recommended for the water to be discharged in the environment. The ratio COD/BOD5 has been determined to vary between 1.25 and 2.80. The results showed that the studied wastewater is a domestic type wastewater composed either by mostly biodegradable pollutants or a mixture of biodegradable and non-biodegradable organic pollutants. These wastewaters constitute therefore a risk for the populations since they are discharged in water bodies without any treatment and used by communities.

Biochemical Methane Potential of Food Wastes from Akouedo Landfill, Côte d’Ivoire

The determination of biochemical methane potential (BMP) is very important for the valorization of food wastes. This study is focused on the evaluation of the theoretical methane production from chemical oxygen demand (COD) of some food wastes, coming out Akouedo landfill. Almost all of the considered samples exhibited methane theoretical yields equal to about 402.5 - 507.8 mLCH4/gVS. These results indicate the suitability of all the studied food wastes from Akouedo landfill to be converted into energy.

Analysis of the Correlation among Three Oxygen Demand Indexes in Surface Water

Based on the monitoring data of chemical oxygen demand(COD),permanganate index(I Mn)and five-day biochemical oxygen demand(BOD 5)of surface water in Tongling section of Yangtze River,the linear relationship among the three indexes in the annual data analysis and the internal reasons,as well as the linear relationship and changes among the three indexes in different seasons were analyzed.The results reveal that in terms of the whole year,COD,I Mn and BOD 5 had a significant correlation and good linear relationship.The fitting slopes of the three indexes were 3.89 of COD/I Mn,4.39 of COD/BOD 5 and 1.16 of I Mn/BOD 5,respectively,which corresponded to the proportional relationship among the three indexes.From the perspective of seasonal changes,there was a very significant correlation between the three indexes in spring and summer.In autumn and winter,only COD and I Mn had a good correlation,but they had a poor correlation with BOD 5.

Chemical oxygen demand oxidation via sustained-release persulfate balls: a rate-compatibility study of flow velocity, releasing, and oxidation

Identification of chemical oxygen demand(COD)in municipal solid waste(MSW)landfill leachates is a challenging problem.This paper investigated the feasibility of using sodium persulfate(PS),a strong oxidant,as a permeable reactive barrier(PRB)filling material.Firstly,sustained-release persulfate balls were manufactured to adjust the release rate of persulfate,the oxidation agent.In addition,Fe(II)-loaded activated carbon(Fe-AC)was used to help with an even distribution of Fe(II)in the porous medium(PRB in this case).Then,the oxidation efficiency and kinetic rate of COD removal by the sustained-release balls were subjected to batch tests.A mass ratio of 1:1.4:0.24:0.7 for PS:cement:sand:water was the most efficient for COD removal(95%).The breakthrough curve for a 5 mm sustained-release ball revealed that the retardation factor was 1.27 and that the hydrodynamic dispersion coefficient was 15.6 cm^(2)/d.The corresponding half-life of COD oxidation was 0.43 d,which was comparable with the half-life of PS release from sustained-release balls(0.56 d).The sustained-release persulfate balls were shown to be an economical material with a simple recipe and production method when catalyzed by Fe-AC.Compared with cutting-edge methods,sustained-release balls used in PRBs offer significant advantages in terms of both effectiveness and economy for the preparation of sustained-release and catalytic materials.These results verified the feasibility of using sustained-release persulfate balls as a PRB material for COD removal.

Photocatalytic Oxidation for Determination of Chemical Oxygen Demand Using Nano-TiO2 Film

A photocatalytic oxidation method for determination of chemical oxygen demand （COD） using nano-TiO2 film, based on the use of a nano-TiO2-Ce（SO4）2 system and electrochemical detection, was proposed. The technique was originated from the direct determination of the Ce（Ⅲ） concentration change resulting from photocatalytic oxidation of organic compounds. Ce（Ⅲ）, which was produced by photocatalytic reduction of Ce（SO4）2, could be measured at a multi-walled carbon nanotubes （MWNT） chemically modified electrode （CME）. The COD values by this method were calculated from the differential pulse voltammetry （DPV） current of Ce（Ⅲ） at the CME. Under the optimal operation conditions, the detection limit of 0.5 mg·L^-1 COD with the linear range of 1-600 mg·L^-1 was achieved. This method was also applied to determination of various COD of ground water and wastewater samples. The resuits were in good agreement with those from the conventional COD methods, i.e., permanganate and dichromate ones.

Excessive greenhouse gas emissions from wastewater treatment plants by using the chemical oxygen demand standard

Chemical oxygen demand(COD)is widely used as an organic pollution indicator in wastewater treatment plants.Large amounts of organic matter are removed during treatment processes to meet environmental standards,and consequently,substantial greenhouse gases(GHGs)such as methane(CH_(4))are released.However,the COD indicator covers a great amount of refractory organic matter that is not a pollutant and could be a potential carbon sink.Here,we collected and analysed COD data from 86 worldwide municipal wastewater treatment plants(WWTPs)and applied a model published by the Intergovernmental Panel on Climate Change to estimate the emission of CH_(4) due to recalcitrant organic compound processing in China’s municipal wastewater treatment systems.Our results showed that the average contribution of refractory COD to total COD removal was55%in 86 WWTPs.The amount of CH_(4) released from the treatment of recalcitrant organic matter in 2018 could have been as high as 38.22 million tons of carbon dioxide equivalent,which amounts to the annual carbon sequestered by China’s wetlands.This suggests that the use of COD as an indicator for organic pollution is undue and needs to be revised to reduce the emission of GHG.In fact,leaving nontoxic recalcitrant organic matter in the wastewater may create a significant carbon sink and will save energy during the treatment process,aiming at carbon neutrality in the wastewater treatment industry.

HACH CODmax在线监测仪及其在环境监测中的应用

HACHCODmax在线监测仪采用当今先进的分析技术,能够连续在线测量,并提供高准确度的结果,符合国家规定的各项技术指标。在实际运行的在线监测和污水处理厂过程控制中发挥重要的作用。

Study on Determination of Chemical Oxygen Demand in Water with Ion Chromatography

A new method for determining chemical oxygen demand （COD） value in water using ion chromatography coupled with nano TiO2-K2S2O8 co-existing system was described. The photocatalytic oxidation system and nano TiO2-K2S2O8 co-existing system could degrade the organic compounds in water. All sulfur-containing species in the reactive solution were eventually transformed to sulfate which could be determined by conductivity detector in ion chromatography. The change of conductivity of sulfate was proportional to COD value. The optimal experimental conditions and the mechanism of the detection were discussed. The application range was 10.0-300.0 mg·L^-1 and the lowest limit of detection was 3.5 mg·L^-1. It was considered that the value obtained could be reliably correlated with the COD value obtained using the conventional methods.

A pilot scale trickling filter with pebble gravel as media and its performance to remove chemical oxygen demand from synthetic brewery wastewater

Evaluating the performance of a biotrickling filter for the treatment of wastewaters produced by a company manufacturing beer was the aim of this study.A pilot scale trickling filter filled with gravel was used as the experimental biofilter.Pilot scale plant experiments were made to evaluate the performance of the trickling filter aerobic and anaerobic biofilm systems for removal of chemical oxygen demand(COD) and nutrients from synthetic brewery wastewater.Performance evaluation data of the trickling filter were generated under different experimental conditions.The trickling filter had an average efficiency of(86.81±6.95)% as the hydraulic loading rate increased from 4.0 to 6.4 m3/(m2·d).Various COD concentrations were used to adjust organic loading rates from 1.5 to 4.5 kg COD/(m3·d).An average COD removal efficiency of(85.10±6.40)% was achieved in all wastewater concentrations at a hydraulic loading of 6.4 m3/(m2·d).The results lead to a design organic load of 1.5 kg COD/(m3·d) to reach an effluent COD in the range of 50–120 mg/L.As can be concluded from the results of this study,organic substances in brewery wastewater can be handled in a cost-effective and environmentally friendly manner using the gravel-filled trickling filter.

A new FTO/TiO_(2)/PbO_(2)electrode for eco-friendly electrochemical determination of chemical oxygen demand

Eco-friendly chemical oxygen demand(COD)sensors are highly desired with respect to the importance of COD determination in environmental protection.In this work,a new FTO/TiO_(2)/PbO_(2)(FTO=fluorine-doped tin oxide)electrode was fabricated with a two-step method and used as an eco-friendly electrochemical COD sensor.The interlayer TiO_(2)was employed to strengthen the adhesion of PbO_(2)on the FTO substrates by providing a large TiO_(2)/PbO_(2)interface area.The effects of the factors including applied potential,supporting electrolyte concentration and stirring speed on the sensing performance were investigated.Under the optimized conditions,linear responses to the COD of water with different COD sources were achieved,and a linear range from 5 to 120 mg/L was obtained in the case of sucrose as the COD source.The relative standard deviations(RSD)were determined to be less than 9%for the glucose solutions with the COD of 7.5,12.5 and 17.5 mg/L.For real sample analysis,the obtained results were comparable with those measured with the conventional dichromate method,with a relative error less than 11%.

基于KPCA-PSO-ELM算法的地表水化学需氧量紫外-可见吸收光谱检测研究

化学需氧量(COD)是水质检测重要指标之一,反映水体有机物含量。传统的COD化学检测方法存在操作繁琐,等待时间长,二次污染等缺点。紫外-可见吸收光谱法是目前水体化学需氧量检测中应用最为广泛的方法之一,具有检测快速、无污染等特点。为了满足地表水化学需氧量快速、实时、在线监测等要求,采用紫外-可见吸收光谱进行测量,提出了内核主成分分析(KPCA)结合粒子群优化极限学习机(PSO-ELM)预测模型,满足当前对地表水化学需氧量快速、实时监测的要求。对光谱进行Savitzky-Golay(SG)滤波以降低随机噪声的影响;用积分光谱代替原光谱,以降低信号波动带来的影响;再将得到的光谱信息归一化,消除不同光谱数据量纲的影响。将预处理后的数据利用KPCA算法将全光谱数据压缩为5个特征,有效解决光谱信息冗余的问题;采用PSO算法对ELM的权重和偏置进行优化极大提高了模型的精度。对217个河流、长江及支流、湖库等地表水样本按照7∶3随机划分成训练集和测试集,并进行建模测试,其中训练集拟合优度(R2)为0.930 2、均方根误差(RMSE)为0.363 0 mg·L^(-1)、测试集拟合优度R2为0.931 9、均方根误差(RMSE)为0.400 7 mg·L^(-1)。为了验证提出的基于KPCA全光谱数据压缩方法对预测模型的提升效果,分别对比了主成分分析(PCA)、连续投影算法(SPA)、套索回归(LASSO)等特征处理算法。PCA-PSO-ELM模型的RMSE为0.715 1 mg·L^(-1)、 SPA-PSO-ELM模型的RMSE为0.473 7 mg·L^(-1)、 LASSO-PSO-ELM模型的RMSE为0.412 6 mg·L^(-1), KPCA-PSO-ELM模型较上述三种模型,RMSE分别降低了78.46%、 18.22%、 2.97%,结果表明KPCA是一种高效的光谱降维算法,能够有效消除光谱冗余信息,提升模型预测精度。基于KPCA-PSO-ELM预测模型结合紫外-可见吸收光谱可以实现对地表水COD快速、实时检测,为在线COD检测场景提供方法支撑。