Average Chemical Oxygen Demand Removal Rate Research Articles

In-situ anaerobic treatment removes the passivation layer of sponge iron to restore the nitrogen and phosphorus removal performance of SBR

Sponge iron (s-Fe0) has a large specific surface area, is cheap and easy to obtain, and has a good reduction capacity. Therefore, its efficacy in enhanced wastewater denitrification and phosphorus removal has been extensively examined. Because of the strong magnetic properties and reactivity of s-Fe0, a passivation layer dominated by iron oxides is formed in liquid phase environments, and this layer inhibits the dissolution of Fe0. In this study, s-Fe0 was used as the carrier filler in an SBR reactor to remove the passivation layer on the surface of s-Fe0 by anaerobic means, and the performance of this reactor was investigated for the removal of chemical oxygen demand (COD), nitrogen, and phosphorus from actual domestic wastewater. The anaerobic treatment of the reactor for 4 days effectively removed the passivation layer on the s-Fe0 surface while the carbon source of the system was maintained with normal feed water. The average removal rates of COD, NH4+-N, and TP in the reactor were 85.67%, 99.8%, and 93.98%, respectively, and the efficient removal of phosphorus in the system was stable for 22–26 days. X-ray diffraction and microbial community analysis showed that, in addition to the formation of FePO4, Fe(PO3), and Fe2P4O12 precipitates were generated in the system to remove phosphorus, and that a synergistic effect aided biological phosphorus removal. Additionally, the presence of abundant microorganisms with corrosion functionality (such as Rhodobacter, Brevundimonas, and Thiobacillus) in the activated sludge system, on the s-Fe0 carrier surface, and inside the carrier, played an essential role in the corrosion and removal of the s-Fe0 passivation layer. These results demonstrated that s-Fe0 is a promising material for nitrogen and phosphorus removal, and anaerobic treatment can effectively alleviate the passivation of s-Fe0. Thus, the efficient removal of phosphorus from actual domestic wastewater can be sustainably achieved.

Pretreatment Hydrolysis Acidification/Two-Stage AO Combination Process to Treat High-Concentration Resin Production Wastewater

The rapid development of the resin industry has led to a large amount of high-concentration resin production wastewater, which has created serious water pollution problems while limiting the development of related enterprises. In this study, a combined pretreatment hydrolysis acidification/two-stage anaerobic oxic (AO) process for high-concentration resin production wastewater was constructed, and the effect of operation time on the treatment efficiency of the hydrolysis acidification and the two-stage AO unit was investigated using chemical oxygen demand (COD), total nitrogen (TN), and NH3-H (ammonia nitrogen) as indicators. The effect of operation time on the treatment efficiency of the hydrolysis acidification and the two-stage AO unit was investigated. Results showed that the pretreatment of “alkaline digestion + ozone oxidation” could effectively remove volatile phenols and phenolic organic pollutants from the wastewater. The average removal rates of COD, TN, and NH3-H (ammonia nitrogen) of resin production were 91.96%, 85.35%, and 85.67%, respectively. The average concentrations of final biochemical effluent were 404.7, 21.4, and 11.4 mg/L, respectively.

A Study of Car Wash Wastewater Treatment by Cyclo-Flow Filtration

With the increase in transportation demand and facilities in this era and the significant improvement in people’s living standards, the annual production and sales of vehicles are steadily increasing. With this, the issues of car wash wastewater treatment and water pollution are becoming more and more serious. Car wash wastewater mainly comprises fine sand, slick oil, suspended solids (SS), and surfactants, and can be quantified as chemical oxygen demand (COD) on a normative basis. This study examines the use of cyclo-flow filtration with high filtrate flux to treat car wash wastewater to solve issue of limited space in metropolitan areas and increase the willingness of the industry to invest in car wash equipment to recover water resources. The average removal rates of SS and COD are about 81% and 43%, respectively. Compared with current technology, the price of recycled water can compensate for operating costs, requiring minimal operating space owing to the single-unit cyclo-flow filtration system.

Removal of organic and nitrogen in a novel anoxic fixed-bed / aerobic fluidized-moving bed integrated with a constructed wetland bio-reactor (A/O-FMCW)

An innovative hybrid process was designed using an integrated bio-reactor based on an anoxic / aerobic process that combined a fixed bed and a fluidized-moving bed with a constructed wetland (A/OFMCW) to enhance the removal of organic material and nitrogen. The goal was to achieve stringent discharge standards for rural domestic wastewater treatment. A preliminary lab-scale investigation of about 130 days obtained an average COD (Chemical Oxygen Demand) removal rate as high as 92.2% at an average influent concentration of 319.5 mg/L. The average TN (Total Nitrogen) removal efficiency positively correlated with the attached-growth biofilm as observed by SEM (Scanning Electron Microscope), and declined from 79.1% to 53.2%. The was accompanied by a gradual increase in the average influent concentration from 16.73 to 52.01 mg/L despite the relative nitrification rate fluctuating between 92.5% and 97.9%. The entire integrated system improved the COD removal efficiency by nearly 36% and the TN by 14–28%. Classical autotrophic nitrification and heterotrophic denitrification were the main mechanisms responsible for the elimination of pollutants, and the latter was determined to be the limiting step. Overall, this study provides an effective and less expensive alternative method to apply or upgrade DWWT (Decentralized Wastewater Treatment).

Performances Analysis of an Upflow Anaerobic Filter for Domestic Sewage Treatment

Upflow anaerobic filter (UAF) with actual domestic wastewater were examined in this study. The Impacts of hydraulic retention time (HRT) on the performance of a UAF and a primary methanogen group were investigated at mesophilic conditions. The chemical oxygen demand (COD) removal rate was more than 75% after 28 days acclimation at 35℃ and HRT of 24 h. With a gradual decrease in the HRT, the COD removal rate first increased and then decreased. When the HRT was 5 h, the COD removal rate was the highest, with an average 81.71% and a maximum of 87.18%. When the HRT decreased to 2.5 h, the average COD removal rate decreased to 75.12%. The methane produced per unit mass of substrate consumed (CH4/CODre) and volume fraction increased with a decrease in HRT. When the HRT was 2.5 h, it reached 0.30 L·g-1, and the volume fraction of methane was maintained at about 73%. The energy generated by the system met the energy demands of the peristaltic pump. Quantitative analysis of the primary methanogen group in the system indicates that Methanosarcinales is the dominant in the system. With a decrease in HRT, the abundances of acetoclastic and hydrogenotrophic methanogens increased significantly.

High efficient alternating anaerobic/aerobic process for polyester resin wastewater treatment: Performance and microbial community structure

This study investigated organics removal and microbial community in a two-stage alternating anaerobic/aerobic (A1/O1/A2/O2) process for polyester resin wastewater treatment. It was found that chemical oxygen demand (COD) concentration could be reduced to below 500 mg L−1 from 12,880 mg L−1 with average COD removal rate of 2.79, 4.37, 0.50 and 0.97 kg m−3 d−1 in four reactors, respectively. Two important chemical compounds in the wastewater, namely, purified terephthalic acid (PTA) (625 mg L−1) and phenol (480 mg L−1), did not display inhibitory effects on COD removal while they were almost completely degraded in the first-stage A/O process. Further, the majority of esters, alkanes, phenols, acids and alcohols could be removed in the system. However, two hazardous refractory compounds, 5,5-dimethyl-1,3-dioxane and 1,4-dioxane, were still present as major components in the final effluent. 16S rRNA high-throughput sequencing results revealed that a distinct preference of selected bacterial groups towards anaerobic/aerobic reactors and operating conditions. High abundance of Lewinella genus (2.4–34.0%), which was correlated to ester-hydrolyzing ability, may play an important role in the high efficiency of organics removal.

Anaerobic treatment of antibiotic production wastewater pretreated with enhanced hydrolysis: Simultaneous reduction of COD and ARGs

The presence of high concentration antibiotics in wastewater can disturb the stability of biological wastewater treatment systems and promote generation of antibiotic resistance genes (ARGs) during the treatment. To solve this problem, a pilot system consisting of enhanced hydrolysis pretreatment and an up-flow anaerobic sludge bed (UASB) reactor in succession was constructed for treating oxytetracycline production wastewater, and the performance was evaluated in a pharmaceutical factory in comparison with a full-scale anaerobic system operated in parallel. After enhanced hydrolysis under conditions of pH 7 and 85 °C for 6 h, oxytetracycline production wastewater with an influent chemical oxygen demand (COD) of 11,086 ± 602 mg L−1 was directly introduced into the pilot UASB reactor. With the effective removal of oxytetracycline and its antibacterial potency (from 874 mg L−1 to less than 0.61 mg L−1 and from 900 mg L−1 to less than 0.84 mg L−1, respectively) by the enhanced hydrolysis pretreatment, an average COD removal rate of 83.2%, 78.5% and 68.9% was achieved at an organic loading rate of 3.3, 4.8 and 5.9 kg COD m−3 d−1, respectively. At the same time, the relative abundances of the total tetracycline (tet) genes and a mobile element (Class 1 integron (intI1)) in anaerobic sludge on day 96 were one order of magnitude lower than those in inoculated sludge on day 0 (P < 0.01). The reduction of ARGs was further demonstrated by metagenomic sequencing. By comparison, the full-scale anaerobic system treating oxytetracycline production wastewater with an influent COD of 3720 ± 128 mg L−1 after dilution exhibited a COD removal of 51 ± 4% at an organic loading rate (OLR) 1.2 ± 0.2 kg m−3 d−1, and a total tet gene abundance in sludge was five times higher than the pilot-scale system (P < 0.01). The above result demonstrated that enhanced hydrolysis as a pretreatment method could enable efficient anaerobic treatment of oxytetracycline production wastewater containing high concentrations of oxytetracycline with significantly lower generation of ARGs.

COD removal efficiency and mechanism of HMBR in high volumetric loading for ship domestic sewage treatment.

The hybrid membrane bioreactor (HMBR) has been applied in ship domestic sewage treatment under high volumetric loading for ship space saving. The mechanism and influence factors on the efficiency, including hydraulic retention time (HRT), dissolved oxygen (DO) of chemical oxygen demand (COD) removal were investigated. The HMBR's average COD removal rate was up to 95.13% on volumetric loading of 2.4 kgCOD/(m3•d) and the COD concentration in the effluent was 48.5 mg/L, far below the International Maritime Organization (IMO) discharge standard of 125 mg/L. DO had a more remarkable effect on the COD removal efficiency than HRT. In addition, HMBR revealed an excellent capability of resisting organics loading impact. Within the range of volumetric loading of 0.72 to 4.8 kg COD/(m3•d), the effluent COD concentration satisfied the discharge requirement of IMO. It was found that the organics degradation in the aeration tank followed the first-order reaction, with obtained kinetic parameters of vmax (2.79 d-1) and Ks (395 mg/L). The original finding of this study had shown the effectiveness of HMBR in organic contaminant degradation at high substrate concentration, which can be used as guidance in the full scale of the design, operation and maintenance of ship domestic sewage treatment devices.

Operation and Performance of Large-Scale MFCs for Treating Brewery Waste

Each year, Americans consume over 6.3 billion gallons of beer. As a result, over 50 billion gallons of brewery wastewater is created annually. Wastewater pre-treatment is an important investment for craft breweries as the biological oxygen demand (BOD) and the total suspended solids (TSS) from the waste stream leaving the brewery have to be significantly reduced before it enters the municipal system. Therefore, the treatment of brewery wastewater is an enormous and expensive part of the environmentally conscious brewing business. Brewery wastewater is characterized with high amounts of sugar, starch, and proteins, which makes it perfect candidate for Microbial Fuel Cell (MFC) application. MFCs have been proven as a promising technology for sustainable wastewater treatment and also as a way for direct recovery of electric energy [1]. In this study, two 10 liter MFCs were used to treat brewery waste collected from Stone Brewery, Escondido, CA. The MFCs had tubular design with a nanofiltration membrane separator, submerged oxygen reducing cathode and carbon cloth anode (Fig. 1). The two reactors were connected in series and operated under continuous flow. The objective of the study was to evaluate the long-term treatment capacity of the MFCs and optimize the operational parameters for maximum volumetric treatment rates and energy recovery. Three main parameters were used to evaluate the MFCs performance. These were chemical oxygen demand (COD) removal, the magnitude of the generated current density and the columbic efficiency (CE) of the COD transformation into electricity. The MFCs had an anode volume of 10L and anode surface area of 65 m2. The first MFC in the series (MFC #1) was first had an inflow of diluted buffered brewery wastewater effluent. MFC #2 was operated with the outflow of MFC #1. The MFCs was continuously running for 250 days when various flow rates of 1ml/min, 2ml/min, 3ml/min and 5ml/min were explored during the study. Over the period of 250 days and loading rates between 1ml/min to 5 ml/min, MFC #1 demonstrated an average COD removal rate of 51.6 ± 19.4%, current density of 2.77 ± 0.99 A/m3 and CE of 8 ± 7%. MFC #2 had an average COD removal of 50.9 ± 20.5%, current density of 2.0 ± 0.6 A/m3 and CE of 14 ± 11% (Fig. 2). Thus the whole system showed an average COD removal of 74.7 ± 19.2%, COD treatment rate of 0.56 ± 0.37 kg-COD/anode-m3-day, CE of 9 ± 6%, and current density of 2.4± 0.6 A/m3. This study demonstrated that MFCs could be useful devices for long-term continuous treatment of brewery wastewater. The system tested is modular, scalable and constructed from cost-effective materials. Future work will include additional large-scale pilot testing and further design and operational optimization to accomplish higher volumetric treatment rates.

Stormwater infiltration and surface runoff pollution reduction performance of permeable pavement layers.

In this paper, the laboratory-scale permeable pavement layers, including a surface permeable brick layer, coarse sand bedding layers (thicknesses = 2, 3.5, and 5 cm), and single-graded gravel sub-base layers (thicknesses = 15, 20, 25, and 30 cm), were built to evaluate stormwater infiltration and surface runoff pollution reduction performance. And, the infiltration rate (I) and concentrations of suspended solids (SS), total phosphorus (TP), chemical oxygen demand (COD), ammonia nitrogen, and total nitrogen (TN) were measured under the simulated rainfall intensity of 72.4 mm/h over duration of 60 min. The results indicate that the thickness factor primarily influences the infiltration rate and pollutant removal rate. The highest steady infiltration rate was for surface brick layer 51.0 mm/h, for 5-cm sand bedding layer 32.3 mm/h, and for 30-cm gravel sub-base layer 42.3 mm/h, respectively. The SS average removal rate was relative higher (79.8 ∼ 98.6 %) for all layers due to the interception and filtration. The average removal rates of TP and COD were for surface layer 71.2 and 24.1 %, for 5-cm bedding layer 54.8 and 9.0 %, and for 20-cm sub-base layer 72.2 and 26.1 %. Ammonia nitrogen and TN cannot steadily be removed by layers according to the experiment results. The optimal thickness of bedding sands was 5 cm, and that of sub-base gravels was 20 ∼ 30 cm.

Nutrient removal and biogas upgrading by integrating freshwater algae cultivation with piggery anaerobic digestate liquid treatment.

An integrated approach that combined freshwater microalgae Scenedesmus obliquus (FACHB-31) cultivation with piggery anaerobic digestate liquid treatment was investigated in this study. The characteristics of algal growth, biogas production, and nutrient removal were examined using photobioreactor bags (PBRbs) to cultivate S. obliquus (FACHB-31) in digestate with various digestate dilutions (the concentration levels of 3200, 2200, 1600, 1200, 800, and 400mgL(-1) chemical oxygen demand (COD)) during 7-day period. The effects of the level of pollutants on nutrient removal efficiency and CO2 removal process were investigated to select the optimum system for effectively upgrade biogas and simultaneously reduce the nutrient content in digestate. The treatment performance displayed that average removal rates of COD, total nitrogen (TN), total phosphorous (TP), and CO2 were 61.58-75.29, 58.39-74.63, 70.09-88.79, and 54.26-73.81%, respectively. All the strains grew well under any the dilution treatments. With increased initial nutrient concentration to a certain range, the CO4 content (v/v) of raw biogas increased. Differences in the biogas enrichment of S. obliquus (FACHB-31) in all treatments mainly resulted from variations in biomass productivity and CO2 uptake. Notably, the diluted digestate sample of 1600mgL(-1) COD provided an optimal nutrient concentration for S. obliquus (FACHB-31) cultivation, where the advantageous nutrient and CO2 removals, as well as the highest productivities of biomass and biogas upgrading, were revealed. Results showed that microalgal biomass production offered real opportunities to address issues such as CO2 sequestration, wastewater treatment, and biogas production.

Effects of Alternating Oxic-Anoxic Model on Nitrite Accumulation in Biological Nitrogen Removal System

The effects of chemical oxygen demand (COD), ammonia nitrogen, total nitrogen removal rates and nitrite accumulation are investigated under alternating oxic-anoxic model in biological nitrogen removal system——sequencing batch reactor (SBR). The system operational effect was studied by analyzing pollutants removal and nitrite accumulation changes. The results showed that the ammonium nitrogen removal rate increased gradually and reached 60% at last. The average removal rate of ammonia nitrogen was 50.2%. The average total nitrogen removal rate was 31.0% due to the low ammonia nitrogen removal and the low carbon in the inflow. The average COD removal rate was 41.7%, finally the COD removal rate reached near 60%. The average nitrite accumulation rate was 68.71%. The alternating oxic-anoxic model reached stable nitrite accumulation.

Biodegradation Performance of an Inner-Loop Three-Phase Fluidized-Bed Bioreactor to Treat Petrochemical Wastewater

In order to remove the petroleum hydrocarbons in petrochemical wastewater, an airlift inner-loop three-phase fluidized-bed (AITF) bioreactor was designed independently, combining the chemical embedding technique to treat petrochemical wastewater continuously. This biological fluidized bed reactor had an excellent antishock ability on the hydraulic loading capacity and the chemical oxygen demand (COD) loading capacity. Moreover, because the microbial biodegradation of petrochemical wastewater was difficult, the reactor also maintained good potential biodegradation capability, and the average COD removal rate was about 87% and average total petroleum hydrocarbons removal rate was about 95% in the steady continuous stage. The volumetric loading capacity of the AITF bioreactor is two to five times of that of traditional activated sludge methods.

Electrochemical treatment of domestic wastewater using boron-doped diamond and nanostructured amorphous carbon electrodes

The performance of the electrochemical oxidation process for efficient treatment of domestic wastewater loaded with organic matter was studied. The process was firstly evaluated in terms of its capability of producing an oxidant agent (H2O2) using amorphous carbon (or carbon felt) as cathode, whereas Ti/BDD electrode was used as anode. Relatively high concentrations of H2O2 (0.064 mM) was produced after 90 min of electrolysis time, at 4.0 A of current intensity and using amorphous carbon at the cathode. Factorial design and central composite design methodologies were successively used to define the optimal operating conditions to reach maximum removal of chemical oxygen demand (COD) and color. Current intensity and electrolysis time were found to influence the removal of COD and color. The contribution of current intensity on the removal of COD and color was around 59.1 and 58.8%, respectively, whereas the contribution of treatment time on the removal of COD and color was around 23.2 and 22.9%, respectively. The electrochemical treatment applied under 3.0 A of current intensity, during 120 min of electrolysis time and using Ti/BDD as anode, was found to be the optimal operating condition in terms of cost/effectiveness. Under these optimal conditions, the average removal rates of COD and color were 78.9 ± 2 and 85.5 ± 2 %, whereas 70% of total organic carbon removal was achieved.

Packed bed up-flow anaerobic sludge blanket combined with multistage sand fine roughing filtration for municipal wastewater treatment and reuse

There is a high potential for reuse of treated wastewater due to the shortage of renewable water resources for agricultural purposes in many countries of the world. To achieve this goal, an integrated anaerobic pilot plant treatment system treating almost 10 m 3 /day of wastewater was designed, manufactured and installed in a nearby wastewater treatment plant. The treatment scheme consists of a packed bed up-fl ow anaerobic sludge blanket (P-UASB) with corrugated lamella sheets, followed by inclined plate settler (IPS). However, to obtain a treated effl uent amenable for reuse, post-treatment was carried out using a multi-stage roughing fi ne fi ltration unit (MSRFF). The pilot plant was operated at average hydraulic fl ow rate of 10 m 3 /day with average organic loading rate of 3.27 kg chemical oxygen demand (COD) m 3 /day. Two retention times in P-UASB namely, 4 and 6 h were investigated. The performance of the treatment scheme was monitored via physico-chemical as well as bacteriological and parasitological analysis. Treatment of wastewater by P-UASB followed by IPS produced a high quality effl uent. Average removal rates of COD, biochemical oxygen demand (BOD) and total suspended solids (TSS) were 75, 70.6 and 91.3, respectively, with average corresponding residual values of 75, 58 and 18 mg/l. However, to obtain sustainable quality of treated effl uent for reuse, post-treatment using MSRFF improved the quality of treated wastewater both chemically and biologically. The average residual concentrations of COD, BOD and TSS were 60, 34 and 10.9 mg/l, respectively, while almost complete removal of Fecal Coliforms was achieved. The treatment scheme proved to be a very promising approach for wastewater treatment for reuse in agricultural purposes.

Mechanism of efficient nutrient removal and microbial analysis of a combined anaerobic baffled reactor–membrane bioreactor process

A combined ABR–MBR process consisting of an anaerobic baffled reactor (ABR) combined with an aerobic membrane bioreactor (MBR) treating municipal wastewater was investigated at controlled pH range 6.5–8.5 and at constant temperature 25 ± 1 °C. Total nitrogen (TN), ammonia (NH4 +–N), total phosphorus (TP), and chemical oxygen demand (COD) removal performances were evaluated by analyzing the mechanism for efficient nutrient removal. The results showed that the average removal rates of COD, NH4 +–N, TN, and TP reached 93, 99, 79, and 92 %, respectively, corresponding with the COD, NH4 +–N, TN, and TP effluent of 24 (18–31), 0.4 (0–0.8), 10.6 (8.8–12.9), and 0.31 (0.1–0.5) mg/L under the operational condition of hydraulic retention time (HRT) 7.5 h, recycle ratio 200 %, and dissolved oxygen 3 mg/L. The MBR enhanced NH4 +–N, TN, and TP removal rates of 13, 10, and 18 %, respectively, and the membrane retention reduced TP 0.17 mg/L. The process was able to maintain a stable performance with high-quality effluent. Analysis of the results by fluorescence in situ hybridization showed that the abundance of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and phosphorus accumulating organisms as percentages of all bacteria in each compartment was stable. The enriched microorganisms in the system appear to be the main drivers of the process efficient for nutrient removal.

Combined Application of UV Photolysis and Ozonation with Biological Aerating Filter in Tertiary Wastewater Treatment

To enhance the biodegradability of residual organic pollutants in secondary effluent of wastewater treatment plants, UV photolysis and ozonation were used in combination as pretreatment before a biological aerating filter (BAF). The results indicated that UV photolysis could not remove much COD (chemical oxygen demand), and the performance of ozonation was better than the former. With UV photolysis combined with ozonation (UV/O3), COD removal was much higher than the sum of that with UV photolysis and ozonation alone, which indicated that UV photolysis could efficiently promote COD removal during ozonation. This pretreatment also improved molecular weight distribution (MWD) and biodegradability greatly. Proportion of organic compounds with molecular weight (MW) &lt;3 kDalton was increased from 51.9% to 85.9%. COD removal rates with BAF and O3/BAF were only about 25% and 38%, respectively. When UV/O3oxidation was combined with BAF, the average COD removal rate reached above 61%, which was about 2.5 times of that with BAF alone. With influent COD ranging from 65 to 84 mg/L, the effluent COD was stably in the scope of 23–31 mg/L. The combination of UV/O3oxidation with BAF was quite efficient in organic pollutants removal for tertiary wastewater treatment.

Continuous electricity generation by a graphite granule baffled air–cathode microbial fuel cell

A baffled air–cathode microbial fuel cell (BAFMFC) was designed and operated under continuous flow. With glucose fed as substrate, an average voltage of 652 mV was obtained under the external resistance of 1000 Ω (30 °C). The maximum power density was 15.2 W/m 3 with the chemical oxygen demand (COD) removal rate of 88.0%. The overall resistance was 13.7 Ω while ohmic internal resistance was 10.8 Ω. Average COD removal rate was 69.7–88.0%, when COD loading varied from 4.11 kg COD/(m 3 NAC d) to 16.0 kg COD/(m 3 NAC d). The liquid from corn stover steam explosion process (COD = 7160 ± 50 mg/L) was treated by BAFMFC, and the maximum power density was 10.7 W/m 3 with the average COD removal rate was 89.1%. The present study indicated BAFMFC can be comparable to the traditional anaerobic baffled reactor in COD removal rate for high-concentration wastewater and have an advantage in energy harvest from wastewater.

Removal of anthraquinone reactive dye from wastewater by batch hydrolytic–aerobic recycling process

The degradation of anthraquinone dye Reactive Blue 19 (RB19) of 600 mg/L in the synthetic wastewater was studied using a biofilm hydrolytic–aerobic recycling process (recycling process). The COD (chemical oxygen demand) and RB19 removal efficiency could be up to 91% and 90% in 24 h, respectively, with the recycling rate being 10 mL/min. When the recycling rates were 8 mL/min and 10 mL/min, the average COD and RB19 removal rate reached the largest values of 109.9 mg/L h and 23.6 mg/L h, respectively. The results also showed that RB19 removal rate in both the hydrolytic and aerobic reactor declined whereas COD removal rate in the aerobic reactor increased with increasing of recycling rate. With the recycling rate of 10 mL/min, VFA (volatile fatty acid) in the wastewater was of the lowest value and pH value was apparently higher than those with other recycling rates. The ratios of VFA/alkalinity were all less than 0.6 when the recycling rate was more than 5 mL/min, which indicated that the activity of hydrolytic microorganisms had not been inhibited and the recycling process maintained a stable condition. Results in this work shown that hydrolytic–aerobic recycling process successfully dealt with the issues of over-acidification and inhibition in the hydrolysis process and effectively enhanced the removal efficiencies of RB19 and COD.

Plant-biofilm oxidation ditch for in situ treatment of polluted waters

Eutrophication of surface water bodies is a problem of increasing environmental and ecological concern worldwide and is particularly serious in China. In the present study, oxidation ditches were connected to a lake receiving municipal sewage sludges. Two 24 m 2 (width 2 m, length 12 m) parallel plastic oxidation ditches material were installed on a lake near the inlet of the municipal sewage. Zizania caduciflora and Canna generalis were grown in the ditches with plastic floating supporters for the removal of N and P from the sewage. The experiment was conducted firstly with municipal sewage in autumn–winter seasons for about 150 days under the following conditions: 2 m 3/h influent flow, 0.75 kW jet-flow aerator (air/water of 5), 18 h HRT (hydrological retention time) and a return ratio of 10. Then it was run with the polluted lake water in summer–autumn for about 160 days with an aerator of 1.25 kW and an influent of 6 m 3/h (air/water 3.3, HRT 6 h). The performance was quite stable during the experimental period for the municipal sewage treatment. The average removal rates of COD (chemical oxygen demand), SS (suspended solids), TP (total phosphorus), NH 4 +-N and inorganic-N were 70.6, 75.8, 72.6, 52.1 and 50.3%, respectively. For the polluted lake water treatment, the average concentrations of COD, NH 4 +-N and TP were 42.7, 13.1 and 1.09 mg/L, respectively, in the influent and were 25.1, 6.4 and 0.38 mg/L, respectively, in the effluent. The capacity of the plants to remove N and P by direct uptake was limited, but the indirect mechanisms also occurred. The proposed process, transforming the natural lake into a wastewater treatment plant, could evidently reduce the costs of the sewage collection, the land space requirement and the construction compared with conventional sewage treatment plants, and is especially suited to conditions in south China and south-east Asia.