Nitrification and denitrification in biological activated carbon filter for treating high ammonia source water

Since the ammonia in the effluent of the traditional water purification process could not meet the supply demand, the advanced treatment of a high concentration of NH₄ ⁺-N micro-polluted source water by biological activated carbon filter (BACF) was tested. The filter was operated in the downflow manner and the results showed that the removing rate of NH₄ ⁺-N was related to the influent concentration of NH₄ ⁺-N. Its removing rate could be higher than 95% when influent concentration was under 1.0 mg/L. It could also decrease with the increasing influent concentration when the NH₄ ⁺-N concentration was in the range from 1.5 to 4.9 mg/L and the dissolved oxygen (DO) in the influent was under 10 mg/L, and the minimum removing rate could be 30%. The key factor of restricting nitrification in BACF was the influent DO. When the influent NH₄ ⁺-N concentration was high, the DO in water was almost depleted entirely by the nitrifying and hetetrophic bacteria in the depth of 0.4 m filter and the filter layer was divided into aerobic and anoxic zones. The nitrification and degradation of organic matters existed in the aerobic zone, while the denitrification occurred in the anoxic zone. Due to the limited carbon source, the denitrification could not be carried out properly, which led to the accumulation of the denitrification intermediates such as NO₂ ^?. In addition to the denitrification bacteria, the nitrification and the heterotrophic bacteria existed in the anoxic zone.     

Water quality prediction of copper-molybdenum mining-beneficiation wastewater based on the PSO-SVR model

● Data acquisition and pre-processing for wastewater treatment were summarized. ● A PSO-SVR model for predicting COD_eff in wastewater was proposed. ● The COD_eff prediction performances of the three models in the paper were compared. ● The COD_eff prediction effects of different models in other studies were discussed. The mining-beneficiation wastewater treatment is highly complex and nonlinear. Various factors like influent quality, flow rate, pH and chemical dose, tend to restrict the effluent effectiveness of mining-beneficiation wastewater treatment. Chemical oxygen demand (COD) is a crucial indicator to measure the quality of mining-beneficiation wastewater. Predicting COD concentration accurately of mining-beneficiation wastewater after treatment is essential for achieving stable and compliant discharge. This reduces environmental risk and significantly improves the discharge quality of wastewater. This paper presents a novel AI algorithm PSO-SVR, to predict water quality. Hyperparameter optimization of our proposed model PSO-SVR, uses particle swarm optimization to improve support vector regression for COD prediction. The generalization capacity tested on out-of-distribution (OOD) data for our PSO-SVR model is strong, with the following performance metrics of root means square error (RMSE) is 1.51, mean absolute error (MAE) is 1.26, and the coefficient of determination (R²) is 0.85. We compare the performance of PSO-SVR model with back propagation neural network (BPNN) and radial basis function neural network (RBFNN) and shows it edges over in terms of the performance metrics of RMSE, MAE and R², and is the best model for COD prediction of mining-beneficiation wastewater. This is because of the less overfitting tendency of PSO-SVR compared with neural network architectures. Our proposed PSO-SVR model is optimum for the prediction of COD in copper-molybdenum mining-beneficiation wastewater treatment. In addition, PSO-SVR can be used to predict COD on a wide variety of wastewater through the process of transfer learning.     

Relationships of nitrous oxide fluxes with water quality parameters in free water surface constructed wetlands

The effects of chemical oxygen demand (COD) concentration in the influent on nitrous oxide (N₂O) emissions, together with the relationships between N₂O and water quality parameters in free water surface constructed wetlands, were investigated with laboratoryscale systems. N₂O emission and purification performance of wastewater were very strongly dependent on COD concentration in the influent, and the total N₂O emission in the system with middle COD influent concentration was the least. The relationships between N₂O and the chemical and physical water quality variables were studied by using principal component scores in multiple linear regression analysis to predict N₂O flux. The multiple linear regression model against principal components indicated that different water parameters affected N₂O flux with different COD concentrations in the influent, but nitrate nitrogen affected N₂O flux in all systems.     

Effect of short-term atrazine addition on the performance of an anaerobic/anoxic/oxic process

In this study, an anaerobic/anoxic/oxic (A²O) wastewater treatment process was implemented to treat domestic wastewater with short-term atrazine addition. The results provided an evaluation on the effects of an accidental pollution on the operation of a wastewater treatment plant (WWTP) in relation to Chemical Oxygen Demand (COD) and biological nutrient removal. Domestic wastewater with atrazine addition in 3 continuous days was treated when steady biological nutrient removal was achieved in the A²O process. The concentrations of atrazine were 15, 10, and 5 mg·L^?1 on days 1, 2 and 3, respectively. The results showed that atrazine addition did not affect the removal of COD. The specific NH₄ ⁺ oxidation rate and NO₃ ^? reduction rate decreased slightly due to the short-term atrazine addition. However, it did not affect the nitrogen removal due to the high nitrification and denitrification capacity of the system. Total nitrogen (TN) removal was steady, and more than 70% was removed during the period studied. The phosphorus removal rate was not affected by the short-term addition of atrazine under the applied experimental conditions. However, more poly-hydroxy-alkanoate (PHA) was generated and utilized during atrazine addition. The results of the oxygen uptake rate (OUR) showed that the respiration of nitrifiers decreased significantly, while the activity of carbon utilizers had no obvious change with the atrazine addition. Atrazine was not removed with the A²O process, even via absorption by the activated sludge in the process of the short-term addition of atrazine.     

A dynamic mathematical model for wastewater stabilization ponds

A dynamic mathematical model was developed to predict the effluent quality of facultative wastewater stabilization ponds. For a sound representation of sediment–water column, water column–atmosphere interactions and stratification due to variations in dissolved oxygen concentrations, a two-dimensional hydraulic model was employed considering dispersed flow and diffusion in horizontal and vertical directions, respectively. Resulting partial differential equation system was solved using finite difference methods and matrix manipulation techniques. The model has been calibrated and evaluated on the basis of collected data from a full-scale facultative stabilization pond in Selçuk, Izmir. Variations of COD, NH₄-N, PO₄-P, dissolved oxygen, bacteria and algae concentrations with time and the dimensions of the pond were estimated by using the dynamic model. The model can be used for design of new stabilization ponds and also, for improving the effluent quality of existing ponds.     

Comparative experiment on treating digested piggery wastewater with a biofilm MBR and conventional MBR: simultaneous removal of nitrogen and antibiotics

A biofilm membrane bioreactor (BF-MBR) and a conventional membrane bioreactor (MBR) were parallelly operated for treating digested piggery wastewater. The removal performance of COD, TN, NH₄ ⁺-N, TP as well as antibiotics were simultaneously studied when the hydraulic retention time (HRT) was gradually shortened from 9 d to 1 d and when the ratio of influent COD to TN was changed. The results showed that the effluent quality in both reactors was poor and unstable at an influent COD/TN ratio of 1.0±0.2. The effluent quality was significantly improved as the influent COD/TN ratio was increased to 2.3±0.5. The averaged removal rates of COD, NH₄ ⁺-N, TN and TP were 92.1%, 97.1%, 35.6% and 54.2%, respectively, in the BF-MBR, significantly higher than the corresponding values of 91.7%, 90.9%, 17.4% and 31.9% in the MBR. Analysis of 11 typical veterinary antibiotics (from the tetracycline, sulfonamide, quinolone, and macrolide families) revealed that the BF-MBR removed more antibiotics than the MBR. Although the antibiotics removal decreased with a shortened HRT, high antibiotics removals of 86.8%, 80.2% and 45.3% were observed in the BF-MBR at HRTof 5–4 d, 3–2 d and 1 d, respectively, while the corresponding values were only 83.8%, 57.0% and 25.5% in the MBR. Moreover, the BF-MBR showed a 15% higher retention rate of antibiotics and consumed 40% less alkalinity than the MBR. Results above suggest that the BF-MBR was more suitable for digested piggery wastewater treatment.

Open image in new window

     

Process evaluation of an alternating aerobic-anoxic process applied in a sequencing batch reactor for nitrogen removal

In order to improve the nitrogen removal efficiency and save operational cost, the feasibility of the alternating aerobic-anoxic process (AAA process) applied in a sequencing batch reactor (SBR) system for nitrogen removal was investigated. Under sufficient influent alkalinity, the AAA process did not have an advantage over one aerobicanoxic (OAA) cycle on treatment efficiency because microorganisms had an adaptive stage at the alternating aerobic-anoxic transition, which would prolong the total cycling time. On the contrary, the AAA process made the system control more complicated. Under deficient influent alkalinity, when compared to OAA, the AAA process improved treatment efficiency and effluent quality with NH₄ ⁺-N in the effluent below the detection limit. In the nitrification, the average stoichiometric ratio between alkalinity consumption and ammonia oxidation is calculated to be 7.07 mg CaCO₃/mg NH₄ ⁺-N. In the denitrification, the average stoichiometric ratio between alkalinity production and NO₃ ^?-N reduction is about 3.57 mg CaCO₃/mg NO₃ ^?-N. As a result, half of the alkalinity previously consumed during the aerobic nitrification was recovered during the subsequent anoxic denitrification period. That was why the higher treatment efficiency in the AAA process was achieved without the supplement of bicarbonate alkalinity. If the lack of alkalinity in the influent was less than 1/3 of that needed, there is no need for external alkalinity addition and treatment efficiency was the same as that under sufficient influent alkalinity. Even if the lack of alkalinity in the influent was more than 1/3 of that needed, the AAA process was an optimal strategy because it reduced the external alkalinity addition and saved on operational cost.     

Enhanced biohydrogen generation from organic wastewater containing NH 4 + by phototrophic bacteria Rhodobacter sphaeroides AR-3

NH ₄ ⁺ is typically an inhibitor to hydrogen production from organic wastewater by photo-bacteria. In this experiment, biohydrogen generation with wild-type anoxygenic phototrophic bacterium Rhodobacter sphaeroideswas found to be sensitive to NH ₄ ⁺ due to the significant inhibition of NH ₄ ⁺ to its nitrogenase. In order to avoid the inhibition of NH ₄ ⁺ to biohydrogen generation by R. sphaeroides, a glutamine auxotrophic mutant R. sphaeroides AR-3 was obtained by mutagenizing with ethyl methane sulfonate. The AR-3 mutant could generate biohydrogen efficiently in the hydrogen production medium with a higher NH ₄ ⁺ concentration, because the inhibition of NH ₄ ⁺ to nitrogenase of AR-3 was released. Under suitable conditions, AR-3 effectively produced biohydrogen from tofu wastewater, which normally contains 50–60 mg/L NH ₄ ⁺ , with an average generation rate of 14.2 mL/L·h. This generation rate was increased by more than 100% compared with that from wild-type R. sphaeroides.     

Fe-pillared bentonite,a stable Fenton catalyst for treatment of petroleum refinery wastewater

Fe-pillared bentonite (Fe-Bent) was prepared by ion exchange as heterogeneous catalyst for degradation of organic contaminants in petroleum refinery wastewater. X-ray diffraction analysis showed the existence of α-Fe₂O₃. The effects of pH, H₂O₂ concentration, and catalyst dosage on the rate of lowering the chemical oxygen demand (COD) were investigated in detail. Removal efficiency of COD can be up to 92% under the following conditions: dosage of Fe-Bent 7 g L^?1, pH value 3, and H₂O₂ concentration 10 mmol L^?1. Fe-Bent showed good stability for the degradation of organics in petroleum refinery wastewater for five cycles. The adsorption of organics in wastewater onto Fe-Bent could be well described by a pseudo-second-order kinetic model.     

Water-level based discrete integrated dynamic control to regulate the flow for sewer-WWTP operation

• A model-free sewer-WWTP integrated control was proposed. • A dynamic discrete control based on the water level was developed. • The approach could improve the sewer operation against flow fluctuation. • The approach could increase transport capacity and enhance pump efficiency. This study aims to propose a multi-point integrated real-time control method based on discrete dynamic water level variations, which can be realized only based on the programmable logic controller (PLC) system without using a complex mathematical model. A discretized water level control model was developed to conduct the real-time control based on data-automation. It combines the upstream pumping stations and the downstream influent pumping systems of wastewater treatment plant (WWTP). The discretized water level control method can regulate dynamic wastewater pumping flow of pumps following the dynamic water level variation in the sewer system. This control method has been successfully applied in practical integrated operations of sewer-WWTP following the sensitive flow disturbances of the sewer system. The operational results showed that the control method could provide a more stabilized regulate pumping flow for treatment process; it can also reduce the occurrence risk of combined sewer overflow (CSO) during heavy rainfall events by increasing transport capacity of pumping station and influent flow in WWTP, which takes full advantage of storage space in the sewer system.     

Circulating fluidized bed biological reactor for nutrients removal

A new biological nitrogen removal process, which is named herein “The circulating fluidized bed bioreactor (CFBBR)”, was developed for simultaneous removal of nitrogen and organic matter. This process was composed of an anaerobic bed (Riser), aerobic bed (Downer) and connecting device. Influent and nitrified liquid from the aerobic bed enters the anaerobic bed from the bottom of the anaerobic bed, completing the removal of nitrogen and organic matter. The system performance under the conditions of different inflow loadings and nitrified liquid recirculation rates ranging from 200% to 600% was examined. From a technical and economic point of view, the optimum nitrified liquid recirculation ratewas 400%. With a shortest total retention time of 2.5 h (0.8 h in the anaerobic bed and 1.5 h in the aerobic bed) and a nitrified liquid recirculation rate of 400% based on the influent flow rate, the average removal efficiencies of total nitrogen (TN) and soluble chemical oxygen demand (SCOD) were found to be 88% and 95%, respectively. The average effluent concentrations of TN and SCOD were 3.5 mg/L and 16 mg/L, respectively. The volatile suspended solid (VSS) concentration, nitrification rate and denitrification rate in the system were less than 1.0 g/L, 0.026-0.1 g NH₄ ⁺-N/g VSS·d, and 0.016–0.074 g NO_x ^?-N/g VSS·d, respectively.     

Model of stomatal ammonia compensation point (STAMP) in relation to the plant nitrogen and carbon metabolisms and environmental conditions

Agricultural crops can be either a source or a sink of ammonia (NH₃). Most NH₃ exchange models developed so far do not account for the plants nitrogen (N) metabolism and use prescribed compensation points. We present here a leaf-scale simplified NH₃ stomatal compensation point model related to the plants N and carbon (C) metabolisms, for C₃ plants. Five compartments are considered: xylem, cytoplasm, apoplasm, vacuole and sub-stomatal cavity. The main processes accounted for are the transport of ammonium (NH₄⁺), NH₃ and nitrate (NO₃⁻) between the different compartments, NH₄⁺ production through photorespiration and NO₃⁻ reduction, NH₄⁺ assimilation, chemical and thermodynamic equilibriums in all the compartments, and stomatal transfer of NH₃.The simulated compensation point is sensitive to paramaters related to the apoplastic compartment: pH, volume and active transport rate. Determining factors are leaf temperature, stomatal conductance and NH₄⁺ flux to the leaf. Atmospheric NH₃ concentration seem to have very little effect on the compensation point in conditions of high N fertilization. Comparison of model outputs to experimental results show that the model underestimates the NH₃ compensation point for high N fertilization and that a better parametrisation of sensitive parameters especially active trasport rate of NH₄⁺ may be required.     

Removing nitrogen and phosphorus from simulated wastewater using algal biofilm technique

Algal biofilmtechnology is a new and advanced wastewater treatment method. Experimental study on removing nitrogen and phosphorus from simulated wastewater using algal biofilm under the continuous light of 3500 Lux in the batch and continuous systems was carried out in this paper to assess the performance of algal biofilm in removing nutrients. The results showed that the effect of removing nitrogen and phosphorus by algal biofilm was remarkable in the batch system. The removal efficiencies of total phosphorus (TP), total nitrogen (TN), ammonia-nitrogen (NH₃-N), and chemical oxygen demand (COD) reached 98.17%, 86.58%, 91.88%, and 97.11%, respectively. In the continuous system, hydraulic retention time (HRT) of 4 days was adopted; the effects of removing TP, TN, NH₃-N, and COD by algal biofilm were very stable. During a run of 24 days, the removal efficiencies of TP, TN, NH₃-N, and COD reached 95.38%, 83.93%, 82.38%, and 92.31%, respectively. This study demonstrates the feasibility of removing nitrogen and phosphorus from simulated wastewater using algal biofilm.     

Anaerobic treatment of wastewater containing methanol in upflow anaerobic sludge bed (UASB) reactor

The direct conversion of methanol into methane is the main process in anaerobic treatment of methanol containing wastewater. However, acetic acid can also be produced from methanol theoretically, which may probably result in an abrupt pH drop and deteriorate the anaerobic process. Therefore, it is interesting to know what would really happen in an anaerobic reactor treating methanol wastewater. In this study, an up-flow anaerobic sludge bed (UASB) reactor treating methanol wastewater was operated. The chemical oxygen demand (COD), acetic acid and pH of the effluent were monitored at different loadings and influent alkalinity. The results showed that the anaerobic reactor could be operated steadily at as low as 119 mg/L of influent alkalinity and high organic loading rate with no obvious pH drops. Volatile fatty acids accumulation was not observed even at strong shock loadings. The microorganisms in the sludge at the end of the test became homogeneous in morphology, which were mainly spherical or spheroidal in shape.     

Performance of an ANAMMOX reactor treating wastewater generated by antibiotic and starch production processes

A pilot-scale anaerobic ammonia oxidation (ANAMMOX) reactor was used to treat mixed wastewater resulting from a chlortetracycline and starch production process. The results, collected over the course of 272 days, show that the ratio of influent ammonium to nitrite, pH, and temperature can all affect the efficiency of nitrogen removal. The ratio of influent ammonium to nitrite was maintained at about 1:1 at a concentration below 200 mg·L^-1 for both influent ammonium and nitrite. The total nitrogen (TN) loading rate was 0.15–0.30 kgN·m^-3·d^-1, pH remained at 7.8–8.5, and temperature was recorded at 33±1°C. The rate of removal of ammonia, nitrite, and TN were over 90%, 90%, and 80%, and the effluent ammonium, nitrite and TN concentrations were below 50, 30, and 100 mg·L^-1.     

Seasonal differences in treatment efficiency of a set of stabilization ponds in a semi-arid region

This article aims to determine the significant differences of the seasonal changes of pH, chemical oxygen demand (COD), biological oxygen demand (BOD), and total suspended solids (TSS) parameters in a wastewater stabilization pond. The variation of these parameters followed the seasonal pattern of temperature. The mean seasonal pH of the influent wastewater ranged between 7.8 (in spring) and 7.9 (in summer), while in the final effluents it was between 7.9 (in winter) and 8.3 (in summer). The mean seasonal COD of the influent wastewater ranged between 650?mg?L^?1 in spring and 600?mg?L^?1 in autumn, whereas in the effluents it was between 150?mg?L^?1 in autumn and 270?mg?L^?1 in spring. The mean seasonal BOD₅ of the influent wastewater ranged between 360?mg?L^?1 in autumn and 390?mg?L^?1 in winter, whereas in the effluents it was between 66?mg?L^?1 in summer and 130?mg?L^?1 in winter. The results showed that the percent removals of COD, BOD₅ and TSS from final effluents were maximum in summer for COD and BOD₅ (76%), summer (83%) and for TSS in winter (78%), respectively. Data analysis showed that there were significant differences between parameters of pH, COD, BOD₅ and TSS at four different seasons (p?相似文献   

Changes in major factors affecting the ecosystem health of the Weihe River in Shaanxi Province, China

Maintenance of the ecosystem health of a river is of great importance for local sustainable development. On the basis of both qualitative and quantitative analysis of the influence of natural variations and human activities on the ecosystem function of the Weihe River, the changes in major factors affecting its ecosystem health are deter- mined, which include： 1） Deficiency of environment flow： since the 1960s, the incoming stream flow shows an obvious decreasing tendency. Even in the low flow period, 80% of the water in the stream is impounded by dams for agriculture irrigation in the Baoji district. As a result, the water flow maintained in the stream for environmental use is very limited. 2） Deterioration of water quality： the concentrations of typical pollutants like Chemical Oxygen Demand （COD） and NH3-N are higher than their maximum values of the Chinese environmental quality standard. Very few fish species can survive in the River. 3） Deformation of water channels： the continuous channel sedimentation has resulted in the decrease in stream gradient, shrinkage of riverbed and the decline in the capability for flood discharge. 4） Loss of riparian vegetation： most riparian land has been occupied by urban construction activities, which have caused the loss of riparian vegetation and biodiversity and further weakened flood control and water purification functions.     

以污水流行病学监测广西某市12个污水处理厂服务区域精神活性物质的消耗量

精神活性物质滥用和使用量逐年递增正成为社会稳定、环境健康新的关注点。准确地估算某一地区这类化合物的消耗总量是管理这类物质的关键。本研究对中国广西某市12个污水处理厂(wastewater treatment plants,WWTPs)服务区域中的8种精神活性物质消耗量进行了调查。首先,采用固相萃取-液相色谱-串联质谱法测定了广西某市12个WWTPs进水中8种精神活性物质的浓度,检测到在<方法检测(method detection limit,MDL)至170.9 ng·L^-1范围内的5种精神活性物质。然后,依据污水流行病学(wastewater-based epidemiology,WBE)进行消耗量反算。结果表明,氯胺酮(ketamine,KET)、吗啡(morphine,MOR)、冰毒(methamphetamine,METH)、摇头丸(3,4-methylenedioxymethamphetamine,MDMA)是主要检出的精神活性物质,平均消耗量分别为682.4、167.8、44.6、11.3 mg·d^-1·1000inh^-1;而可卡因(cocaine,COC)、苯甲酰爱康宁(benzoylecgonine,BE)、甲卡西酮(methcathinone,MC)没有被检出。对WWTPs进水中精神活性物质的残留进行分析,估算这些物质在特定区域的消耗量,为防控风险提供支持。     

A novel polyacrylonitrile–zeolite nanocomposite to clean Cs and Sr from radioactive waste

Radioactive wastes containing Cs⁺ and Sr²⁺ are among the most dangerous environmental pollutants. Therefore, removing Cs⁺ and Sr²⁺ from environmental media is needed. Removal can be done by nanocrystalline ion exchangers. Nanocrystalline ion exchangers are studied in depth for the treatment of nuclear wastes because these exchangers have high exchange capacity and fast kinetics. However, operating the columns of these exchangers is very difficult. This issue may be overcome by the preparation and use of nanocomposites. Here, we prepared a novel polyacrylonitrile–zeolite nanocomposite for the removal of Cs⁺ and Sr²⁺ in a fixed-bed column operation. We studied the effect of influent flow rate, nanocomposite bed height and initial concentrations. Experimental data were analysed using the Thomas model and the bed-depth service time model. The results reveal that total adsorbed ion and bed capacity increased with increasing initial ions concentration and bed height; and decreased with increasing influent flow rate. The maximum bed capacity was 0.085 meq/g for Cs⁺ and 0.128 meq/g for Sr²⁺. The critical bed height (Z ₀) was 4.35 cm for Cs⁺ and 2.89 cm for Sr²⁺. These findings demonstrate that the new nanocomposite is suitable for removal of Cs⁺ and Sr²⁺.     

Protoplast fusion between Saccharomyces cerevisiae and Rhodobacter sphaeroides for the treatment of soybean wastewater

The kinetic parameters and the purification rates of the hybrid cell Foaz in soybean processing wastewater (SPW) were measured through a shaking reaction and in two automatic regulated control stable fermentation systems (ARCSFS). The maximum specific growth rate of Foaz was 0.576 h^‐1, higher than that of one of its parental strains Rhodobacter sphaeroides P9479 and lower than that of another parental strain Saccharomyces cerevisiae Y9407. The BOD₅ removal rate of Foaz in the No. 1 system was 61.3%, higher than those of both its parental strains when the influent BOD₅ concentration was 4600 mg/L. The results of this study suggest that the hybrid Foaz has a better capacity of the degradation of organic pollutants in SPW than its parental strains and it may be applicable to the treatment of high concentration organic wastewater.