Full-scale trials of recycled glass as tertiary filter medium for wastewater treatment

Pilot-scale trials at a domestic wastewater treatment works compared the performance of three grades of recycled glass (coarse, medium and fine) when used as tertiary filter media for total suspended solids removal (TSS). Fine glass produced the best effluent quality but blinded rapidly and coarse glass could process three times the flow but with a reduction in final effluent quality. The medium glass offered a compromise with similar flow characteristics to the coarse glass, yet still achieve good solids removal, albeit less than the fine glass. Full-scale studies compared the performance of medium glass with the sand medium that is typically used in this application. There was little difference between them in terms of TSS removal, and they both removed around 75% of TSS from the influent, provided that the solids concentration did not exceed 70mg/l. However, the glass media had superior flow characteristics and was able to treat an additional 8-10% of the influent following the backwash cycle. Over the study period, the influent to the filters had an average TSS concentration of 38mg/l and produced an effluent with an average of 15mg TSS/l. In order to design for an average TSS concentration of 20mg/l, the maximum solids loading on the medium should not exceed 0.25kg solids/m(3)/h. Selecting recycled glass as a tertiary filter medium will give a 10% reduction in the amount of media required, compared to sand. It also carries with it the benefits of using a recycled material, and although these are more difficult to quantify they include: reduced CO(2) emissions and use of a more sustainable product that promotes favourable publicity and positive environmental reporting.     

Operational Experience with Biological Aerated Filters1

Yorkshire Water has two full-scale biological aerated filters in operation. The first was installed at North Bierley sewage-treatment works for the tertiary nitrification of humus―tank effluent to secure consent compliance and ascertain if anticipated future standards could be achieved. The second was recently commissioned at Hedon sewage-treatment works for secondary treatment, as part of an evaluation of compact plant to meet the requirements of the urban waste water treatment Directive at coastal sites. The plant at North Bierley (near Bradford) is constructed mainly of steel and is designed to achieve an effluent quality of 10 mg/l suspended solids, 10 mg/l BOD, and 5 mg/l ammoniacal nitrogen. The plant at Hedon (near Hull) is constructed of concrete and is designed to achieve a 30 mg/l suspended solids and 25 mg/l BOD standard. Both plants have proved to be capable of meeting their respective effluent requirement. For each works, the paper describes (i) the identification of the problem, (ii) the reasons for selecting the biological aerated filter process, (iii) details of the plant, (iv) operating experiences, and (v) plant performance.     

Treatment using reverse osmosis of an effluent from stainless steel manufacture

Reverse osmosis (RO) and physical/chemical technology were evaluated for treatment of neutralized spent acid effluent (seepage) containing high concentration levels of TDS (7500 mg/l), Ca (400 mg/l), Cr^VI (42 mg/l), nitrate-nitrogen (827 mg/l), ammonia-nitrogen (33 mg/l), fluoride (13 mg/l), phenolics (45 mg/l) and COD (620 mg/l). The calcium concentration level in the seepage could be reduced from approximately 400 to 5 mg/l with soda ash softening. Initial permeate flux (feed and bleed system, 85% water recovery) was 278 l/m²·d. Permeate flux, however, dropped rapidly in the beginning of the run and then remained approximately constant to the end of the run. However, chemical cleaning of the membranes was necessary to maintain flux. The TDS of the RO feed could be reduced in one case from 34,253 to 1560 mg/l (95.5% removal) at 85% water recovery. Nitrate and ammonia nitrogen were reduced from 2691 and 103 mg/l to 414 (84.6% removal) and 15 mg/l (85.3% removal), respectively. Chromium^VI and fluoride were reduced from 183 and 90 mg/l to 0.38 (99.8% removal) and 2.8 mg/l (96.9% removal), respectively. COD removals varied between 60 and 80%. No phenolics, however, could be removed from the feed (approximately 32 mg/l) with the cellulose acetate RO membranes. Phenolics, however, could be effectively removed (<0.2 mg/l) from the RO permeate with hydrogen peroxide oxidation or ion-exchange treatment. Preliminary test work has shown that it should be possible to treat the seepage effectively with RO for pollution control, effluent volume reduction and water recovery. Capital costs for a 600 kl/d plant for lime softening, RO and oxidation equipment are estimated at U.S. $58,000, U.S. $350,000 and U.S. $87,500, respectively.     

HPB工艺用于污水厂提标扩容改造的生产性试验研究

基于HPB工艺中试研究结果,为进一步验证HPB工艺在提标扩容实际生产工况下的处理效果和可实施性,在湖南某水质净化厂进行了生产性试验。试验期间,在总进、出水量保持不变的条件下,进行HPB工艺改造,将现状两组生化池(A2/O)切换为单组运行,处理水量提升1倍,总停留时间缩短为5. 0 h以下。通过复合粉末载体的投加及排泥过程中载体和附着微生物的回收循环,实现了"双泥龄",克服了脱氮菌和除磷菌的污泥龄矛盾,提高了脱氮除磷效率。试验结果表明,生化池混合液浓度控制在10 000 mg/L左右,在厂区进水水量和水质变化较大(K_Z≥1. 3)、水温低于冬季设计温度时,HPB工艺系统运行稳定,主要出水水质指标COD <30 mg/L、NH3-N <1. 5 mg/L、TN <10 mg/L、TP <0. 3 mg/L,能够实现高效、稳定达标。     

Integrated biological and physiochemical treatment process for nitrate and fluoride removal

The feasibility of an integrated biological and physiochemical water treatment process for nitrate and fluoride removal has been evaluated. It consisted of two sequencing batch reactors (SBRs) in series. Performance of the process in the treatment of 24 synthetic water samples having nitrate concentrations of 40, 80, 120, 160, 200, and 250 mg/l (as N) and fluoride concentrations of 6, 10, 15, and 20 mg/l at different combinations was studied. Denitrification followed by defluoridation proved to be the best sequence of treatment. In all cases nitrate could be reduced to an acceptable level of less than 10 mg/l (as N) at 3, 5, and 7 h hydraulic retention times (HRTs) depending on its initial concentration. Fluoride concentrations up to 15 mg/l associated with nitrate concentrations up to 80 mg/l (as N) could be reduced acceptable 1.5 mg/l by alum-PAC slurry using alum doses up 850 mg/l [as Al2(SO4)3 x 16H2O] along with 100 mg/l of powdered activated carbon (PAC). Additional alkalinity produced during denitrification was used up during defluoridation for maintenance of pH avoiding the need for lime addition. On the other hand, residual organics, turbidity, and sulfide present in the denitrified water are removed by alum and PAC at the defluoridation stage along with fluoride, eliminating the need for an additional post-treatment step. At higher nitrate concentrations (> or = 120 mg/l as N), the alkalinity produced at the denitrification stage was in the range of 715-1175 mg/l as CaCO3. This excessive alkalinity inhibited reduction of fluoride to the level of 1.5 mg/l at the defluoridation stage, using alum doses up to 900 mg/l along with 100 mg/l of PAC. In all cases a fluoride concentration of 20 mg/l in water could not be reduced to the acceptable level of 1.5 mg/l.     

Operation of Submerged Filters by Anglian Water Services Ltd

Since the introduction of submerged filters for sewage treatment in Europe, process improvements have been rapid. Downflow submerged filters using natural medium have been superseded by upflow filters using synthetic floating medium. Many advantages have been claimed for these systems and Anglian Water have investigated the operation of the Biobed and Filtabed submerged filters for carbonaceous oxidation, nitrification and suspended-solids removal. The process is based on the use of a bed of floating plastic beads (2–5 mm) through which the sewage flows in an upward direction. The reactor is aerated or non-aerated according to the required application. Results have shown the process to be capable of producing an effluent containing less than 2 mg/l amm.N and 5 mg/l SS. Backwash water requirements are less than 1%. The Biobead/Filtabead systems are designed to be competitive with regard to area, capital and operating costs.     

Pharmaceuticals and personal care products (PPCPs) in surface and treated waters of Louisiana,USA and Ontario,Canada

A newly developed analytical method was used to measure concentrations of nine pharmaceuticals and personal care products (PPCPs) in samples from two surface water bodies, a sewage treatment plant effluent and various stages of a drinking water treatment plant in Louisiana, USA, and from one surface water body, a drinking water treatment plant and a pilot plant in Ontario, Canada. The analytical method provides for simultaneous extraction and quantification of the following broad range of PPCPs and endocrine-disrupting chemicals: naproxen; ibuprofen; estrone; 17beta-estradiol; bisphenol A; clorophene; triclosan; fluoxetine; and clofibric acid. Naproxen was detected in Louisiana sewage treatment plant effluent at 81-106 ng/l and Louisiana and Ontario surface waters at 22-107 ng/l. Triclosan was detected in Louisiana sewage treatment plant effluent at 10-21 ng/l. Of the three surface waters sampled, clofibric acid was detected in Detroit River water at 103 ng/l, but not in Mississippi River or Lake Pontchartrain waters. None of the other target analytes were detected above their method detection limits. Based on results at various stages of treatment, conventional drinking-water treatment processes (coagulation, flocculation and sedimentation) plus continuous addition of powdered activated carbon at a dosage of 2 mg/l did not remove naproxen from Mississippi River waters. However, chlorination, ozonation and dual media filtration processes reduced the concentration of naproxen below detection in Mississippi River and Detroit River waters and reduced clofibric acid in Detroit River waters. Results of this study demonstrate that existing water treatment technologies can effectively remove certain PPCPs. In addition, our study demonstrates the importance of obtaining data on removal mechanisms and byproducts associated with PPCPs and other endocrine-disrupting chemicals in drinking water and sewage treatment processes.     

VALIDATION OF BNR (BIOLOGICAL NUTRIENT REMOVAL) PLANT

Llangefni WwTW receives discharge from the rural town of Llangefni and the local industrial estate and to date this is the first and only BNR plant in Wales. The consents from March 2003 included a reduction in ammonia (NH₄_N) to 1.5 mg/l, suspended solids to 20 mg/l (SS) and Biological Oxygen Demand (BOD) to 7 mg/l and included a new Phosphate (PO₄_P) standard of 2 mg/l. The process selected to meet the new consents was Biological Nutrient Removal (BNR) and was unusual as it was for a small, rural wastewater treatment plant that receives about 26% of its flow from an industrial estate.
During commissioning, the plant produced an average phosphate concentration of 1.0 mg/l and an ammonia concentration of 0.7 mg/l. It was confirmed that to achieve consistent phosphate removal a BOD:P ratio greater than 20:1 is required along with a high VFA (Volatile Fatty Acids) concentration of 200–300 mg/l.     

Comparison of RBC and SBR Systems for the Treatment of Sewage from Small Communities

This paper describes a study which was carried out to evaluate the performance of two types of small sewage-treatment plant which are commonly available in the UK, i.e. a rotating biological contactor and a sequencing batch reactor. Both systems produced an effluent quality of less than 20 mg/l BOD and 30 mg/l SS; however, the sequencing batch reactor was more consistent in producing a better effluent (i.e. BOD<10 mg/l and SS<20 mg/l) than the rotating biological contactor. The sequencing batch reactor also demonstrated a greater tendency to remove nutrients, although the special design features which were used in this study were believed to have enhanced the rate of nutrient removal     

Dissolved organic compounds in reused process water for steam-assisted gravity drainage oil sands extraction

The in situ oil sands production method called steam-assisted gravity drainage (SAGD) reuses process wastewater following treatment. However, the treatment and reuse processes concentrate contaminants in the process water. To determine the concentration and dynamics of inorganic and organic contaminants, makeup water and process water from six process steps were sampled at a facility employing the SAGD process in Alberta, Canada. In the groundwater used for the makeup water, the total dissolved organic carbon (DOC) content was 4 mg/L. This significantly increased to 508 mg/L in the produced water, followed by a gradual increase with successive steps in subsequent water treatments. The concentrations and dynamics of DOC constituents in the process water determined by gas chromatography-mass spectrometry showed that in the produced water, volatile organic compounds (VOCs) such as acetone (33.1 mg/L) and 2-butanone (13.4 mg/L) predominated, and there were significant amounts of phenolic compounds (total 9.8 mg/L) and organic acids including naphthenic acids (NAs) corresponding to the formula C_nH_2n+ZO_X for combinations of n = 4 to 18, Z = 0 and −2, and X = 2 to 4 (53 mg/L) with trace amounts of polycyclic aromatic hydrocarbons (PAHs) such as naphthalene and phenanthrene. No organic contaminants, except for saturated fatty acids, were detected in the groundwater. The concentration of DOC in the recycled water was 4.4-fold higher than that in the produced water. Likewise, the total concentrations of phenols and organic acids in the recycled water were 1.7- and 4.5-fold higher than in the produced water, whereas the total concentrations of VOCs and PAHs in the recycled water were reduced by over 80%, suggesting that phenols and organic acids are selectively concentrated in the process water treatment. This comprehensive chemical analysis thus identified organic constituents that were concentrated in the process water and which interfere with subsequent water treatments in the SAGD process.     

温州北山河黑臭河水治理工程

针对温州北山河黑臭河水COD高达1550mg／L的现状，采用厌氧生物膜床结合水生植物带工艺进行治理。结果表明，该综合治理工艺对COD、N，N-二甲基甲酰胺（DMF）、NH3-N的去除率分别达85％、99％、54．1％以上，治理后不但黑臭完全消除，而且河水具有一定的自净能力。该工艺具有处理效果稳定、造价低、操作方便和维护费用低等优点。     

Seasonal variation of microcystin concentrations in the Saint-Caprais reservoir (France) and their removal in a small full-scale treatment plant

At the Saint-Caprais reservoir (France), a mono-specific bloom of Aphanizomenon flos-aquae occurs every year in the autumn months. Levels of microcystin-LR (MCYST-LR) in this reservoir were evaluated by protein phosphatase type 2A (PP2A) inhibition test as MCYST-LR equivalents in both raw and drinking water. Analysis by HPLC of the crude extract of the mono-specific bloom of A. flos-aquae revealed the presence of MCYST-LR with a low concentration of 270.3 +/- 20.4 ng/g wet weight. MCYST-LR equivalent concentrations in raw water were correlated with the cyanobacteria biomass and they varied between 14 and 74 ng/l. The removal of A. flos-aquae and microcystins were evaluated in a small full-scale plant associated with the Saint-Caprais reservoir. Total elimination of cyanobacterial cells and the low concentration of hepatotoxins was achieved through the combined action of pre-ozonation at 0.07 mg/l and adsorption on powdered activated carbon at 20 mg/l. However, pre-chlorination at 0.42 mg/l followed by 20 mg/l of powdered activated carbon removed only 45% of hepatotoxins.     

再生混凝土的冻融循环试验研究

为了进一步研究再生混凝土耐久性的各种指标,对再生混凝土的冻融循环抵抗性做了基础性试验研究.试验以100%再生骨料替代天然碎石和砂子制备再生混凝土,以水灰比0.45,0.55为变动因素.试验结果表明,100%再生混凝土试件的冻融循环抵抗性与粗、细骨料置换率为0的普通混凝土试件相比,当水灰比为0.45,0.55时其耐久性指数分别降低6%和10%,但都能满足评价混凝土冻融循环抵抗性的最低指标.     

Seawater denitrification in a closed mesocosm by a submerged moving bed biofilm reactor

The performance of a submerged moving bed biofilm reactor (MBBR) for the denitrification of seawater in a 3.25 million closed circuit mesocosm was investigated at pilot scale, using methanol as a carbon source at various C/N ratios. Nitrate accumulation in closed systems where water changes are expensive and problematic may cause toxicity problems to marine life. Seawater was pretreated in a recirculated fixed bed to remove oxygen prior to the denitrification step. The 110l MBBR was partly filled (25%) with spherical positively buoyant polyethylene carriers with an effective surface area of approximately 100 m2 m(-3), which represents 35% of the total surface area. Carriers were maintained submerged by a conical grid and circulated by the downflow jet of an eductor. The MBBR mixing system was designed to prevent dead mixing zones and carrier fouling to avoid sulfate reduction while treating seawater containing as high as 2150 mg SO4-Sl(-1). NO3-N reduction from 53 to as low as 1.7+/-0.7 mg l(-1) and a maximum denitrification rate of 17.7+/-1.4 g Nm(-2) d(-1) were achieved at 4.2-4.3 applied COD/N (w/w) ratio. Methanol consumption corresponded to denitrification stoichiometric values, indicating the absence of sulfate reduction. Denitrification rates and effluent residual dissolved organic carbon were proportional to the C/N ratio. Such reactors could be scaled up in closed systems where water changes must be minimized.     

An evaluation of a hybrid ion exchange electrodialysis process in the recovery of heavy metals from simulated dilute industrial wastewater

Hybrid ion exchange electrodialysis, also called electrodeionization (IXED), is a technology in which a conventional ion exchange (IX) is combined with electrodialysis (ED) to intensify mass transfer and to increase the limiting current density and therefore to carry out the treatment process more effectively. It allows the purification of metal-containing waters, as well as the production of concentrated metal salt solutions, which could be recycled. The objective of this paper was to investigate the ability of the IXED technique for the treatment of acidified copper sulphate solutions simulating rinsing water of copper plating lines. A single-stage IXED process at lab-scale with a small bed of ion exchanger resin with a uniform composition was evaluated, and the treatment performance of the process was thoroughly investigated. The IXED stack was assembled as a bed layered with the ion exchanger resin (strong acid cation-exchange Dowex™) and inert materials. The stack configuration was designed to prevent a non-uniform distribution of the current in the bed and to allow faster establishment of steady-state in the cell for IXED operation. The influence of operating conditions (e.g. ion exchanger resin with a cross-linking degree from 2 to 8% DVB, and current density) on IXED performance was examined. A response surface methodology (RSM) was used to evaluate the effects of the processing parameters of IXED on (i) the abatement yield of the metal cation, which is a fundamental purification parameter and an excellent indicator of the extent of IXED, (ii) the current yield or the efficiency of copper transport induced by the electrical field and (iii) the energy consumption. The experimental results showed that the performance at steady-state of the IXED operation with a layered bed remained modest, because of the small dimension of the bed and notably the current efficiency varied from 25 to 47% depending on the conditions applied. The feasibility of using the IXED in operations for removal of heavy metals from moderately dilute rinsing waters was successfully demonstrated.     

Effects of submerged macrophytes on sediment resuspension and internal phosphorus loading in Lake Hiidenvesi (southern Finland)

The effects of submerged macrophytes on sediment resuspension and internal phosphorus loading in the shallow Kirkkoj?rvi basin of Lake Hiidenvesi were studied by sedimentation traps and sediment and water samples. During the 83 d study period, 793 g DW m(-2) of sediment was resuspended within the stand formed by Ranunculus circinatus, Ceratophyllum demersum and Potamogeton obtusifolius. Outside the stand, 1701g DW m(-2) sediment resuspension was measured during the same period. Water turbidity and concentration of suspended solids (SS) were significantly lower within the plant bed compared with the surrounding water area. Despite the higher concentration of inorganic suspendoids, the concentration of chlorophyll a was higher in the open water than within the submerged plant bed, owing to the enhanced nutrient recycling rate in the absence of submerged plants. With the resuspended sediment, 11.8 mg Pm(-2)d(-1) was brought into the water column within the stand and 24.5 mg Pm(-2)d(-1) outside the stand. Within the macrophyte stand, resuspended particles absorbed phosphorus from the water (indicated by the inverse relationship between SS and soluble reactive phosphorus), which was probably connected to the lowered phosphorus concentration of surface sediment due to uptake by macrophytes.     

Factors affecting removal of selenate in agricultural drainage water utilizing rice straw

Microbial reduction of selenate [Se(VI)] to elemental selenium [Se(0)] is a useful technique for removing Se from agricultural drainage water. A series of batch experiments were conducted in the laboratory to determine the effects of pH (5-10), NO(3)(-) (100-500 mg/l), and SO(4)(2-) (0-5000 mg/l) on the removal of Se(VI) from drainage water with 1000 microg/l of Se(VI) and different amounts (1-4 g) of rice straw. Results showed that rice straw was very effective in creating a reducing environment (Eh=-205 to -355 mV) in the first 3 days of the pH-effect experiments. The optimum conditions for rapid Se(VI) removal from drainage water were a pH range of 6-9, high amounts of SO(4)(2-) (1000-5000 mg/l), low amounts of NO(3)(-) (100 mg/l) and high amounts of rice straw (3-4 g). Under these conditions, it took 5-7 days to reduce 93-95% of the added Se(VI) to Se(0). This study indicates that rice straw may be an inexpensive reducing agent to remediate Se(VI)-dominant San Joaquin Valley drainage water in the field.     

Arsenic Removal from Water Supplies in Northern Chile Using Ferric Chloride Coagulation

Many raw waters in the arid North of Chile contain high concentrations of arsenic (0.1–1.0 mg/l) and, during the 1970s, drinking-water treatment using coagulation was introduced in an attempt to comply with the Chilean standard of 0.05 mg/l. The new World Health Organization recommendation of 0.01 mg/1 for drinking water has led to efforts to enhance arsenic removal.
This paper describes pilot-plant experiments which were carried out to optimize removal by varying the ferric chloride coagulant dose (3–9 mg/1 Fe) and pH value (pH 5.5–8.0) in a raw water which contained an average arsenic concentration of 0.44 mg/l. At pH 5.5, arsenic adsorption was best; however, a pH of 6.5 was considered to be the most suitable for treatment when considering floc elimination. An empirical formula to predict residual arsenic under different operational conditions was obtained and this was confirmed by data collected at a full-scale water-treatment plant.     

植生性再生混凝土的制备及研究

利用再生骨料配制植生性再生混凝土,探讨了植生性再生混凝土配合比设计方案和制备工艺,并选择高羊茅、早熟禾两种植物进行植生相容性试验.结果表明:利用10～20mm的再生骨料、水灰比为0.28、浆骨比0.20、硅粉掺量5%,混凝土设计强度10MPa、孔隙率为25%、pH值12以下、混凝土厚度为6 cm时,高羊茅可以穿透混凝土层,并在室外环境下生长良好.