Effect of powdered activated carbon on Chinese traditional medicine wastewater treatment in submerged membrane bioreactor with electronic control backwashing

Chinese traditional medicine wastewater, rich in macromolecule and easy to foam in aerobic biodegradation such as Glycosides, was treated by two identical bench-scale aerobic submerged membrane bioreactors （SMBRs） operated in parallel under the same feed, equipped with the same electronic control backwashing device. One was used as the control SMBR （CSMBR） while the other was dosed with powdered activated carbon （PAC） （PAC-amended SMBR, PSMBR）. The backwashing interval was 5 min. One suction period was about 90 min by adjusting preestablished backwashing vacuum and pump frequency. The average flux of CSMBR during a steady periodic state of 24 d （576 h） was 5.87 L/h with average hydraulic residence time （HRT） of 5.97 h and that of PSMBR during a steady periodic state of 30 d （720 h） was 5.85 L/h with average HRT of 5.99 h. The average total chemical oxygen demand （COD） removal efficiency of CSMBR was 89.29% with average organic loading rate （OLR） at 4.16 kg COD/（m^3.d） while that of PSMBR was 89.79% with average OLR at 5.50 kg COD/（m^3.d）. COD concentration in the effluent of both SMBRs achieved the second level of the general wastewater effluent standard GB8978-1996 for the raw medicine material industry （300 mg/L）. Hence, SMBR with electronic control backwashing was a viable process for medium-strength Chinese traditional medicine wastewater treatment. Moreover, the increasing rates of preestablished backwashing vacuum, pump frequency, and vacuum and flux loss caused by mixed liquor in PSMBR all lagged compared to those in CSMBR; thus the actual operating time of the PSMBR system without membrane cleaning was extended by up to 1.25 times in contrast with the CSMBR system, and the average total COD removal efficiency of PSMBR was enhanced with higher average OLR.

Application of a novel backwashing process in upflow biological aerated filter

To improve the efficiency of backwashing in upflow biological aerated filter （BAF）, a novel backwashing process named air-water siphon backwashing （AWSB） was proposed and applied on laboratory scale. The effects of backwashing on turbidity and suspended solid （SS） in backwashing efluent using this new backwashing process were compared with those of traditional backwashing process, namely air-water backwashing （AWB）. In AWB, the turbidity of backwashing efluent maintained 100 NUT when consumed 60 min and 10.5 L water. However, in AWSB, it declined to 44 NUT, consumed 40 min, and 7 L water. The COD removal of BAF after backwashing was also analyzed. The average removal rate of COD in the reactor backwashed by AWB and AWSB was 89.34% and 90.91%, respectively. Compared with AWB, the backwashing interval had been prolonged 35%. The volume of backwashing water in that AWSB was only 66.7% of that in AWB. The results demonstrated that AWSB required less water and took shorter backwashing timerelative to AWB to achieve the same turbidity of backwashing efluent, and AWSB was more effective in removing fouling than that of AWB. More significant advantage of AWSB was that the backwashing interval was effectively prolonged

Membrane Fouling Alleviation by Chemically Enhanced Backwashing in Treating Algae-Containing Surface Water: From Bench-Scale to Full-Scale Application

Ultrafiltration(UF)has been increasingly implemented in drinking water treatment plants;however,algae and their secretions can cause severe membrane fouling and pose great challenges to UF in practice.In this study,a simple and practical chemically enhanced backwashing(CEB)process was developed to address such issues using various cleaning reagents,including sodium hypochlorite(NaClO),sodium chloride(NaCl),sodium hydroxide(NaOH),sodium citrate,and their combinations.The results indicate that the type of chemical played a fundamental role in alleviating the hydraulically irreversible membrane fouling(HIMF),with NaClO as the best-performing reagent,followed by NaCl.Furthermore,a CEB process using a combination of NaClO with NaCl,NaOH,or sodium citrate delivered little improvement in the alleviation of membrane fouling compared with NaClO alone.The optimized dosage and dosing frequency of NaClO were 10 mg·L^(-1) two times per day.Long-term pilot-scale and full-scale experiments further verified the feasibility of the CEB process in relieving algae-derived membrane fouling.Compared with the conventional hydraulic backwashing without chemical involvement,the CEB process can effectively remove the organic foulants including biopolymers,humic substances,and proteinlike substances by means of oxidization,thereby weakening the cohesive forces between the organic foulants and the membrane surface.Therefore,the CEB process can efficiently alleviate the algae-related membrane fouling with lower chemical consumption,and is proposed as an alternative to control membrane fouling in treating the algae-containing surface water.

Biomass and microbial activity in a biofilter during backwashing

Biomass and microbial activity in backwashing processes of a biofilter for tertiary treatment were investigated. The microbial groups revealed new distribution along the biofilter depth after low flow rate backwashing for a short time. Then the start-up process was accelerated by backwashing. The biomass profile and microbial activity profile both varying with depth before and after backwashing, can be mathematically described by quadratic equations. Using the profiles, the difference of oxygen demand can be calculated to determine the airflow rate during backwashing. Combined with the difference between biofilters and rapid gravity filters, analysis of biomass and microbial activity can determine more accurately the required airflow rate during backwashing.

Simultaneous Carbon and Nitrogen Removal in Wastewater Treatment Using a Partially Packed Biological Aerated Filter （BAF） without Backwashing Process

Biological aerated filter （BAF） is an advanced oxidation process that can sustain high volumetric loads with high quality effluent. However, backwashing process needed for the system limits its applicability. This study is to investigate the possibility of removing carbon and nitrogen simultaneously in a biological aerated filter （BAF） with partially packed media without any backwashing process. The upper part of BAF up to 0.5 m depth is packed with plastic media （Kaldnes K1） with diameter and length of 10 mm and 7 mm respectively. This partially packed BAF creates a hybrid system of attached growth and suspended growth combined in a single reactor. Three C：N ratios, i.e. 15, 10 and 4, were compared during this study by varying the nitrogen loading while the carbon loading was kept constant at 1.0±0.54 kg COD/（m^3·d）. The organic loading rate （OLR） ratios were calculated based on carbon and TKN loading. The carbon removal percentage of 86.7±7.3%, 85.1±10.3%, and 91.0±5.6% and TKN removal percentage of 24.7±11.6%, 48.0±25.9% and 62.8±7.9% were achieved after steady-state for the C：N ratio of 15, 10, and 4 respectively. Suspended solid concentration in the effluent was found to be high throughout the treatment, but no clogging occurred during the 4 months of operation period even though backwashing was eliminated.

Backwash Effects of Language Testing in EFL Classrooms

The article presents some major researches concerning the concept of backwash effect of language testing; analyses both the positive and negative effects and their implications in EFL classrooms; then provides some suggested ways to be followed when creating positive backwash effects on teaching and learning.

高职英语教学的测试体系与评价

针对目前我国高职英语教学普遍存在的应试教育现象，分析了教学测试体系对英语教学实施的强导向和质量监控作用。应结合教学理论和实践，建立和完善科学合理的教学测试体系，对英语教学质量进行有效监控，使评估更好地促进教学。

On Communicative Reading Testing of College English

Tests are indispensable in the teaching process. A good test can be used as a valuable teaching device. Reading is a major way of acquiring knowledge and it is one of the most important skills in English learning. Then how we can construct a good reading test is the focus for many language researchers. This paper discusses the communicative reading testing of college English and its backwash on teaching.

A Study on the Backwash Effect of the Reform of TEM-8 on Advanced English Course

TEM-8,which aims at testing students’integrated abilities of English,is more and more highly valued.Advanced Eng-lish,with its core teaching aim of cultivating this ability,should have high-quality teaching and optimized test as its objectives.Thus the test and the course can bring out the best in each other.

A pilot scale anoxic/oxic membrane bioreactor(A/O MBR) for woolen mill dyeing wastewater treatment

A pilot scale(10 m 3/d) anoxic/oxic membrane bioreactor(A/O MBR) was tested for dyeing wastewater treatment of woolen mill without wasting sludge in 125 days operation. Results showed that the effluent quality was excellent, i.e. effluent COD less than 25 mg/L, BOD 5 under 5 mg/L, turbidity lower than 0 65 NTU, and colour less than 30 DT, and met with the reuse water standard of China. The removal rates of COD, BOD 5, colour, and turbidity were 92 4%, 98 4%, 74% and 98 9%, respectively. Constant flux operation mode was carried out in this study, and backwash was effective for reducing membrane fouling and maintaining constant flux. Membrane fouling had heavy impact on energy consumption. More attention should be paid on pipe selection and design for the sidestream MBR system, too.

Wash water in waterworks:contaminants and process options for reclamation

Reclamation of clean water from filter backwash water was studied through pilot-scale experiments.The pilot plant consisted of clarification,sand-filtration,and ultrafiltration modules in sequence,with a provision to bypass the sand filter.Clean water that conformed to World Health Organization (WHO) guidelines on Potable Quality was reclaimed.Turbidity,aluminum and iron were found to be critical contaminants in process selection and design.Clarification,followed by sand filtration,was found to be the minim...

Promoting Positive Backwash on Practical English Test for Colleges

Practical English Test for Colleges (PRETCO) is a large-scale national standardized EFL test for the students of higher vocational colleges,postsecondary specialized colleges,and colleges for adults.This thesis is for a preliminary research of PRETCO backwash based on previous studies from home and abroad,making use of their research methods and models.It attempts to explore the aspects of practical English learning of students from higher vocational colleges (HVC) influenced by PRETCO,and the nature of the backwash.Based on the results reported in the study,the writer analyzes the factors inducing negative backwash and puts forward some suggestions for promoting positive one.

A Study and Evaluation of CET-SET for Chinese College Students

Having been implemented since the year 1987, College English Test(CET) is now a national English test used to measure college students' English language competence and promote English language teaching and learning in classrooms. And later in 1999 national CTE committee launched College English Test-Spoken English Test(CET-SET) and started to include speaking as one part but not a compulsory part of this assessment. Now still only a small group of candidates can take CET- SET,which suggested by many researchers could bring harmful backwash to classroom teaching. Therefore, this paper presents a study and evaluation of CET-SET for college students in China. It mainly divides into four parts. Part one gives an introduction about the teaching contexts of college students and their needs for English study. Part two discusses the harmful backwash from CET as well as the reasons and needs to introduce and recommend CET-SET. The third part sheds light on the strengths of CETSET including its beneficial backwash, the test format and the scoring system. The last part talks about its weakness and provide some suggestions and modifications.

Recycling of Mud Derived from Backwash Wastewater Coagulation as Magnetic Sodalite Sphere for Zn^(2+) Adsorption

Herein,we reported a method to prepare magnetic sodalite sphere by using the mud from backwash wastewater after polyaluminum chloride(PAC)coagulation.The results showed that approximately 100%of Fe in the wastewater was precipitated as flocculent iron mud(FM)by adding PAC.FM was converted to spherical magnetic sodalite(FMP)with a diameter of 3μm via a facile alkali hydrothermal method without adding Al/Si resources or reductant.The product FMP had the saturated magnetization of 10.9 emu g^(-1) and high Zn^(2+)adsorption capacity of 50.6 mg g^(-1).Without coagulation with PAC,the removal rate of Fe from the wastewater was only 92.7%,and the precipitated mud(RM)was converted to irregular particles(RMP),which had weak magnetic response and low capacity of Zn^(2+)adsorption comparing with FMP.With the method,the Fe in backwash wastewater was effectively recycled,and the generated sludge was converted to well-formed sodalite sphere without generating any secondary waste.

Application of Submerged Ultrafiltration in Pretreatment of Flue Gas Desulfurization Wastewater

Nowadays,the zero liquid discharge of flue gas desulfurization(FGD)wastewater from coal-fired units has attracted the attention of all countries in the world.The pretreatment methods generally have the problems of high operation cost,small treatment capacity,and poor flexibility.However,the membrane method can avoid the above problems.In the current research,it has not been found that someone directly uses submerged ultrafiltration to pretreat FGD wastewater.Therefore,this paper innovatively proposed to directly use ceramic ultrafiltration membrane to treat FGD wastewater,which can ensure effluent quality and improve the flexibility of the pretreatment system.In this paper,the performance of submerged ultrafiltration membrane for the filtration of FGD wastewater from a power plant was studied to optimize the filtration performance and improve the effluent quality.The effects of operating parameters such as membrane permeate flux,aeration rate and filtration/backwashing time combination on the membrane performance were studied.The results showed that when the filtration/backwashing time combination was 15 min/30 s,with the increased in permeate flux from 55 L/(m2·h)to 100 L/(m2·h),the steady transmembrane pressure(TMP)increased from 39 kPa to 70 kPa,and the fouling rate increased significantly from 4.5 kPa/h to 7.3 kPa/h;When the aeration rate increased from 10 m3/(m2·h)to 30 m3/(m2·h),the membrane pollution was much reduced.Excessive aeration rate cannot further alleviate the membrane pollution,but also brought greater energy consumption;Increasing backwashing time can effectively inhibit the formation of gel layer on the surface of the membrane and prolong the initial stage of low-pressure operation;The rejection of suspended solids(SS)and turbidity of the equipment studied in this paper can reach more than 99%under various working conditions,which can satisfy the water quality requirements of the subsequent steps.The submerged ultrafiltration membrane was suitable for the pretreatment of FGD wastewater because it can ensure the quality of permeate under the premise of long-term operation.

Treatment of submerged hollow fiber ultrafiltration membrane for reuse of sludge water

To lower the costs of wastewater treatment, the submerged hollow fiber ultrafiltration membrane was employed to reuse the filter backwash water and settling tank sludge water. Experimental study indicates that the submerged hollow fiber uhrafihration membrane can condense the concentration of sludge from 0. 1% -0. 3% to 2.5%. At 20 ℃, the system can operate continuously for 80 clays with daily online backwashing with chemical additions only once, and the membrane flux can be recovered up to 97% by using NaClO and NaOH as chemical additions. The results show that the membrane flux is mainly affected by temperature,and has a positive lin- ear relation to temperature with a slope of 0. 368. After treated by submerged hollow fiber uhrafihration membrane, the effluent can reach the National Standard for Drinking Water（ GB5749 -85 ） , especially for the sludge water from sedimentation tanks and the backwashing Water from filters in water supply plants.

Fouling Characteristics and Prevention Techniques for Membrane Bioreactor

Membrane fouling is the main problem of membrane bioreactors (MBR), which seriously influ- ences its wastewater treatment effect and running. The characteristics of microbiology and hydrodynamics concerning membrane fouling were investigated and the measure was put forward for optimum operation of MBR. The measure is that 1) the parameters of activated sludge concentration (X) and membrane flux should be lower than the critical values of X and membrane flux respectively, and 2) the activated sludge should be discharged periodically. The experimental results show that the combination backwashing of gas and perme- ated effluent is better than single gas backwashing or single permeated effluent backwashing. This technique can remove the cake layer deposited on the membrane surface, decrease the membrane fouling, and recover the membrane flux effectively. So it is effective for prevention of membrane fouling.

Research on Backwash Effect of Formative Evaluation in Oral English Learning in Vocational Colleges

The evaluation model which is dominated by formative evaluation can help the teacher diagnose the teaching activity in the process of students learning and timely find the problems, which can timely correct and control the teaching and learning strategies. The questionnaire survey, oral English test, experimental research design and practice prove that establishing a dynamically professional oral English formative evaluation based on student behavior not only has good backwash effect, ensure the enthusiasm and interest of students learning oral English, but also can enhance the autonomic learning awareness and ability of students and improve the cooperative learning and communicative ability of students, which greatly improve the learning effect of students.

Factors to Give Full Play to the Positive Backwash Effect in the Language Testing

＂Backwash＂ has usually been described in terms of the effect of testing on language teaching and learning. ＂Backwash can be harmful or beneficial＂, as Arthur Hughes states. （Hughes： 1989） This paper set out to see how far this term can be applied to the ways in which both the students and teachers can benefit from language testing.

Impacts of backwashing on micropollutant removal and associated microbial assembly processes in sand filters

Backwashing is crucial for preventing clogging of sand filters.However,few studies have investigated the effect of backwashing on micropollutant removal and the dynamic changes in the microbial community in sand filters.Here,we used a series of manganese and quartz sand filters under empty bed contact times(EBCTs)of 2 h and 4 h to explore variations in micropollutant degradation and temporal dynamics of the microbial community after backwashing.The results showed that the removal efficiencies of caffeine,sulfamethoxazole,sulfadiazine,trimethoprim,atrazine,and active biomass recovered within 2 d after backwashing in both types of sand filters at 2-h EBCT,but the recovery of sulfadiazine and trimethoprim was not observed at 4-h EBCT.Moreover,the removal efficiency of atenolol increased after backwashing in the manganese sand filters,whereas maintained almost complete removal efficiency in the quartz sand filters at both EBCTs.Pearson correlation analysis indicated that microbial community composition gradually recovered to the pre-backwashing level(R increased from 0.53 to 0.97)at 2-h EBCT,but shifted at 4-h EBCT(R<0.25)after backwashing.Furthermore,the compositions of the recovered,depleted,and improved groups of microbes were distinguished by applying hierarchical clustering to the differentially abundant amplicon sequence variants.The cumulative relative abundance of recovered microbes at 2-h EBCT was 82.76%±0.43%and 46.82%±4.34%in the manganese and quartz sand filters,respectively.In contrast,at 4-h EBCT,the recovered microbes dropped to 15.55%–25.69%in both types of sand filters.