Algae removal by fine sand/silt filtration

A laboratory scale study was undertaken to determine the potential of a method of filtering algae from water using fine sand/silt as the filter media. Five median sand sizes (0.064–0.335 mm) and four bed depths (3.175–12.700 mm) were examined in constant head experiments with the algae Scenedesmus quadricauda. A total of 46 experiments were conducted with continuous measurements of filtration rate, head loss and effluent quality. All media with median sand sizes at or below 0.200 mm gave consistently high algae removal rates. The average removal was 97.27% (based on fluorescence) with a low average initial head loss across the filter media of 7.3 cm (median grain size diameter of 0.200 mm with the bed depth of 3.175 mm). Initial filtration rates obtained in the experimental apparatus were as high as 226 m³ m⁻²–day⁻¹ (3.84 gpm ft⁻²), comparable to conventional sand units. Run times were short due to surface clogging of the media. No chemical addition was required to obtain high removal levels.     

The removal of virus by a pilot treatment plant

The effect of a pilot water treatment plant upon naturally occurring and artificially high levels of bacteriophages and enteroviruses was investigated. The individual stages studied were flocculation and sedimentation, rapid sand filtration, an activated carbon column and a final chlorination stage. The flocculation and sedimentation unit was consistently effective with an average removal of 99.7 ± 0.3%. The efficiency of the rapid sand filter and the activated carbon column was dependent upon the frequency of back-washing. Both of these units were less effective when recently back-washed and in such cases their percentage removal was negligible when compared with the flocculation and sedimentation unit. The final chlorination unit was found to be very effective, and viruses could not be isolated after this stage provided that a residual free chlorine concentration of 0.4 mg l⁻¹ was maintained.Examination of the data for the plant as a whole revealed that it was capable of removing greater than 99.9995% of any influent viruses.     

Inactivation des virus dans l'eau sur une filiere de production a ozonation etagee

The removal and inactivation of indigenous viruses for individual water treatment processes were investigated both in a pilot (3 m³ h⁻¹) and a full-scale (4000 m³ h⁻¹) plant, treating water from the Seine and Oise rivers respectively.Viruses were recovered by the previously described methods of adsorption-elution using electronegative Balston filters (Joret and Block, 1981) for the pilot plant study or alternatively using either electronegative or electropositive 1 MDS Cuno filters (Sobsey and Glass, 1981) for the full-scale water supply.Depending on the efficiency of filtration, the volumes of water samples concentrated directly in the field varied from 30 to 100 litres for raw, preozonated, stored river water and decanted water, and from 550 to 1000 litres for treated water downstream from the clarification step. BGM cells were used for virus detection by the plaque assay method.During this study, the initial virus concentration in the Seine river water entering the pilot plant, varied from 190 to 1420 PFU/1000 l. The virus removal observed after coagulation-flocculation with 35–50 g m⁻³ of water aluminum chloride (WAC) (a basic aluminum chloride) and settling, was 31–90% effective (130–390 PFU/1000 l. of decanted water), and did not exceed 1–2 logarithms after sand filtration at a rate of 5 m h⁻¹ (83% of 600–800 samples were positive for viruses, maximum concentration = 80 PFU/1000 l.).The preozonation of river water (0.8 ppm during 2–3 min without residual oxidant) inactivated 64–97% of viruses (maximum viral concentration in preozonated water being 300 PFU/1000 l.). Under these conditions, no viruses could be isolated from samples of 550–1000 litres of sand filtered water.The treatment process for the industrial water supply located at Mery sur Oise was preozonation (0.5–1 ppm for 1 min), storage, coagulation-flocculation, settling, sand filtration, second stage ozonation (1.4–1.6 ppm for 10 min, residual oxidant: traces to 0.3 ppm), activated carbon filtration, postozonation (0.4 ppm free residual for 4 min) and chlorine dioxide (0.1 ppm). Nine series of samples were taken after various stages of treatment and tested for viruses. All samples of raw river water yielded positive results with relatively low numbers (10–146 PFU/1000 l.) compared with the number of enterovirus in the Seine river.The efficiency of preozonation before storage could not be evaluated in this study due to its intermittent operation. Enteroviruses were found in 83% of samples after storage (7–100 PFU/1000 l.), 77% after settling and 55% after sand filtration (3–10 PFU/1000 l.). Enteroviruses were not detected after the second stage ozonation in any of the nine samples. The subsequent postozonation and final treatment with chlorine dioxide serves as an additional barrier to ensure virologically safe drinking water.During studies on pilot and full scale water treatment plants, viral isolates are as follows: ECHO virus (49 and 37% respectively), coxsackie B virus (42 and 49% respectively) and poliomyelitis virus (9 and 14% respectively).     

强化常规工艺对三卤甲烷前体物的去除效果研究

分别通过小试和生产性试验研究了强化混凝和强化过滤对三卤甲烷前体物的去除效果。结果表明,强化混凝能有效提高三卤甲烷前体物的去除效果,两组试验去除率最高分别可提高至50.62%和44.75%;相对石英砂滤池,采用炭砂滤池和活性无烟煤滤池进行强化过滤可将三卤甲烷前体物的去除率提高10%~20%,强化过滤出水加氯消毒后三卤甲烷生成总量比石英砂滤池出水低30%~40%,强化过滤后三卤甲烷生成风险显著降低。     

Alum clarification for improving wastewater effluent quality

This paper presents results of an investigation on the application of alum for improving the overall performance of wastewater treatment plants. These studies were conducted on a pilot scale of 7200 gal day⁻¹. The pilot plant incorporated parallel systems for evaluating conventional and high-rate clarification. The conventional system included chemical addition, rapid mix, flocculation, sedimentation, and rapid sand filtration. The high-rate system differed in that the flocculated solids were introduced directly onto a dual-media filter with no intermediate sedimentation.Results of this study indicate that in both types of tertiary clarification treatment, greater than 95 per cent removal of the BOD of a nitrified secondary effluent, turbidity, and suspended solids were achieved with alum doses of 40–60 mg 1⁻¹. Efficient phosphorus removals were also realized in the same systems by increasing the alum dose to about 150 mg 1⁻¹. In addition to the removal of BOD and phosphorus, bacteria and heavy metals were removed.     

复合污染地下水的两级处理工艺中试研究

开展了石英砂+生物活性炭的两级处理工艺净化复合污染地下水的中试研究。结果表明,当石英砂滤料未成熟时,单级过滤对铁、锰的去除效果较好,但是对氨氮及CODMn的去除效果不理想;二级过滤工艺可以明显提高水中氨氮和CODMn的去除效果;滤料成熟后系统对铁、锰、氨氮及CODMn的平均去除率分别达到99.5%,99.9%,93.7%和34.5%。该处理工艺出水水质较好,抗水质冲击负荷能力强,且运行稳定性高。     

Removal of nitrogen, phosphorus and COD from waste water using sand filtration system with Phragmites Australis

The removal efficiencies of nitrogen, phosphorus and COD from waste water were examined using sand filtration systems with Phragmites australis (Cav.) Trin. ex. Steudel. The quality of effluent waters from the system with plant were far better than those from the one without plant, implying Phragmites could incorporate nitrogen and phosphorus into its tissues and promote phosphorus absorption onto the sand by the release of oxygen from the roots. The P-pot provided with the influent containing 198 mg l^- of total nitrogen and 21 mg l^-1 of total phosphorus had the highest biomass of Phragmites. Harvestable above-ground biomass accounted for about 3.5 kg m^-2 and removable nitrogen and phosphorus accounted for 69 and 6 g m^-2 respectively.The removal rates of total nitrogen and phosphorus in the system with Phragmites receiving variable amounts of COD were almost at the same level and also much better than those of the systems without plant, implying that the different COD concentrations in the influent media do not impair the removal efficiencies of nitrogen and phosphorus. Also Phragmites was found to resist COD concentration as high as 128 mg l^-1, and signs of clogging were not detected in this system throughout the experiment.     

Slow sand filtration as a technique for the tertiary treatment of municipal sewages

The investigation was designed to demonstrate the viability, or otherwise, of slow sand filtration as a means of tertiary treatment for secondary effluents derived from conventional aerobic, biological treatment processes operating with municipal wastewaters. Secondary effluents derived from both an activated-sludge plant and from a percolating filtration plant were employed.The basic slow sand filtration unit used consisted of a 140 mm i.d. perspex cylinder, 2.65 m in height containing a 950 mm depth of fine sand. Treatment rates were either 3.5 or 7.0 m d⁻¹ and the sand used was of an effective size initially of 0.3 mm and then later of 0.6 mm.This investigation has demonstrated that a laboratory-scale slow sand filtration unit is capable of consistently removing at least 90% of the suspended solids, more than 65% of the remaining BOD and over 95% of the coliform organisms from the settled effluent from an operational percolating filter plant. The length of operational run averaged 20 days at 3.5 m d⁻¹ and 13 days at 7.0 m d⁻¹. Slightly inferior results were achieved when using the settled effluent from an operational activated sludge unit.Further investigation employing a horizontal-flow gravel pre-filter demonstrated that at flows of 2 m h⁻¹ with a contact time of 33 min up to 82% of the suspended solids in the secondary effluent could be removed prior even to slow sand filtration.     

Silage effluent digestion by an upflow anaerobic filter

Silage effluent is generally regarded as one of the major agricultural pollutants of water courses. Efficient anaerobic digestion of silage effluent was achieved by a 3-day hydraulic retention in an upflow anaerobic filter. The filter was a laboratory scale unit containing a limestone chip support matrix. At loading rates ranging from 7.8 to 14.2 kg COD m⁻³ active volume day⁻¹, the average COD removal obtained ranged from 86 to 89% with a TOA removal of 82–88%. The methane content of the biogas produced ranged from 81 to 88%. The rate of COD conversion to CH₄ was independent of the loading rate under the conditions tested and the observed efficiency averaged 0.357 m¹ CH₄(STP) kg⁻¹ COD introduced to the reactor.The reactor tolerated considerable variation in influent pH without any apparent decrease in digestion efficiency. It is apparent from the results obtained that a reactor which is in routine use for slurry digestion may also be utilised for silage effluent digestion on a seasonal basis.     

Slow sand filters effectively reduce Phytophthora after a pathogen switch from Fusarium and a simulated pump failure

Slow sand filtration has been shown to effectively reduce Phytophthora zoospores in irrigation water. This experiment tested the reduction of Phytophthora colony forming units (CFUs) by slow sand filtration systems after switching the pathogen contaminating plant leachate from Fusarium to Phytophthora and the resilience of the system to a short period without water, as might be caused by a pump failure. The slow sand filtration system greatly reduced Phytophthora CFUs and transmission after switching the pathogens. In addition, Phytophthora reduction by the slow sand filter was equally effective before and after the simulated pump failure. Reduction of Fusarium was not seen by the SSFs, before or after the simulated pump failure. The results suggest that slow sand filters are effective at reducing larger organisms, such as Phytophthora zoospores, even after a pump failure or a change in pathogens.     

Leachate treatment with nitrification of ammonia

Results are presented on the treatment of leachate to remove ammonia by biological nitrification. Outdoor activated sludge and trickling filter pilot plants were operated for 2 years at a major co-disposal landfill. Leachate ammonia nitrogen concentrations ranged from 150 to 550 mg l^?1 while TOC concentrations ranged from 200 to 500 mg l^?1. Very little of the TOC was degradable and BOD: NH₃-N ratios were typically 1:3.Nitrification was successfully established in both plants, and curves were established for the response of the kinetics to different temperatures. Maximum ammonia removal rate in the activated sludge plant was at least 131 g N kg VSS^?1 day^?1 achieved at an average temperature of 13°C. Maximum removal rate in the trickling filter was 309 mg N m^?2 day^?1, at 16°C.Operating problems and strategies for full-scale treatment are discussed.     

On‐site wastewater treatment using reactive filter media

The aim of this study is to reduce the phosphate concentration in treated wastewater using a small amount of the reactive filter media, Filtralite P. Biologically treated wastewater was passed through a filter with 215 g of Filtralite P. In the laboratory, the phosphate removal efficiency was 51% at a flow speed of 0.87 m/h. Under real conditions, in an experimental stand filled with 0.5 m³ of Filtralite P, the phosphate removal efficiency was 85% and the removal efficiency of total suspended solids was 57% after a 5‐month period. The residual phosphate concentration in the filtrate from the experimental stand was 1 mg/L of PO₄‐P after the 5‐month period. The experimental filtration plant was buried in the ground, and it did not freeze and worked well under winter conditions. The results of this study can be useful in the design and development of tertiary wastewater treatment plants in view of their sustainability potential.     

As oxidation by Thiomonas arsenivorans in up-flow fixed-bed reactors coupled to As sequestration onto zero-valent iron-coated sand

The combined processes of biological As^III oxidation and removal of As^III and As^V by zero-valent iron were investigated with synthetic water containing high As^III concentration (10 mg L⁻¹). Two up-flow fixed-bed reactors (R1 and R2) were filled with 2 L of sieved sand (d = 3 ± 1 mm) while zero-valent iron powder (d = 76 μm; 1% (w/w) of sand) was mixed evenly with sand in R2. Thiomonas arsenivorans was inoculated in the two reactors. The pilot unit was studied for 33 days, with HRT of 4 and 1 h. The maximal As^III oxidation rate was 8.36 mg h⁻¹ L⁻¹ in R1 and about 45% of total As was removed in R2 for an HRT of 1 h. A first order model fitted well with the As^III concentration evolution at the different levels in R1. At the end of the pilot monitoring, batch tests were conducted with support collected at different levels in R1. They showed that bacterial As^III oxidation rate was correlated with the axial length of reactor, which could be explained by biomass distribution in reactor or by bacterial activity. In opposition, As^III oxidation rate was not stable in R2 due to the simultaneous bacterial As^III oxidation and chemical removal by zero-valent iron and its oxidant products. However, a durable removal of total As was realized and zero-valent iron was not saturated by As over 33 days in R2. Furthermore, the influence of zero-valent iron and its oxidant corrosion products on the evolution of As^III-oxidizing bacteria diversity was highlighted by the molecular fingerprinting method of PCR-DGGE using aoxB gene as a functional marker of aerobic As^III oxidizers.     

Improving removal of turbidity causing materials by using polymers as a filter aid

With recognizing that particles represent transport vehicles for undesirable chemical contaminants, and potentially disease causing microbial pathogens, the removal of particle materials becomes important to protect the public health. However, due to the complicated filtration mechanisms and interactions between the polymer and particles, the selection of polymers currently remains empirical. This study was initiated to investigate the feasibility of the use of polymers as filter aids for water containing lime softening particles; explore the roles of polymer characteristics in the filtration process; and examine major factors affecting the performance of polymer aided filtration. Seven representative polymers with different molecular weights and charges were tested using a declining rate filter pilot plant. The results show that at a starting flow rate of 15 m/h, the removal of turbidity particles could be significantly improved by using polymers as a filter aid. It was also found that the impacts of initial filter ripening could be substantially reduced and no turbidity breakthrough was observed after 3 days of operation. However, the use of polymer might significantly increase the filtration headloss, especially for the polymers with high molecular weight. To produce a high quality filtrate while ensuring the acceptable filtration productivity, low or moderately low molecular weight polymers are recommended. For a low molecular weight polymer, its optimum mixing intensity and polymer dose were found around 700 s⁻¹ and 0.01 mg/l, respectively. On the basis of the results and particle properties, it is believed that interparticle bridging is the dominant mechanism underlying the interactions between polymers and lime softening particles.     

Removal of asbestos fibres from potable water by coagulation and filtration

There is growing concern that asbestos-like fibres in drinking water could be a potential health hazard. Methods are described for removing asbestiform fibres from potable water based on modifications to conventional water treatment techniques. These include simple sand filtration, diatomaceous earth filtration, chemical coagulation or combinations of these depending on the degree of removal required. The most effective method, involving chemical coagulation with iron salts and polyelectrolytes followed by filtration, resulted in better than 99·8% fibre removal from water containing 12 x 10⁶ fibres 1⁻¹.     

陶粒生物滤池与无烟煤滤池强化过滤效果对比

以北京某自来水厂处理密云水库蓄水的出水（混凝沉后水）为试验用水，通过中试对比研究了陶粒生物滤池与无烟煤滤池的过滤效果。结果表明，陶粒生物滤池与无烟煤滤池对水中颗粒物的去除效果接近；对于水中的浊度，无烟煤滤层对其去除效果较好，而陶粒滤层的过滤效果则较差，需要依靠石英砂的截污作用来降低浊度；陶粒对有机物的过滤效果优于无烟煤的，陶粒生物滤池对TOC的去除率为14．9％～30．2％，对CODMn的去除率为13．1％～38．5％；与无烟煤滤池相比，陶粒生物滤池具有水头损失增长快、周期较短、初滤水中颗粒物较多等缺点。     

高铁矿井水回用处理工艺研究

针对韩桥矿高铁矿井水质,考察了混凝＋沉淀＋过滤回用处理工艺除铁的最佳运行条件。结果表明,以聚合氯化铝（PAC）作为混凝剂,最佳投药量为80mg／L时,铁的去除率可达到91％;选择天然锰砂作为滤料,滤速在8～10m／h,进水pH值高于6．05,滤层高度大于75cm时,锰砂除铁效果较好,出水铁含量在0．1mg／L以下,可以满足《城市污水再生利用工业回用水水质》（GB／T19923--2005）中的限值要求。     

Simulated Cryptosporidium removal under swimming pool filtration conditions

There has been no information available on the removal of Cryptosporidium oocysts or oocyst‐sized particles under the sand filtration conditions normally used for swimming pool water treatment. A pilot sand filtration plant has therefore been constructed at The University of Wales Swansea and operated under swimming pool conditions (25 m/h downflow, 30°C, 1.5 mg/L free chlorine, pH 7.3 to 7.5, alkalinity 120–150 mg/L as calcium carbonate). Removal of fluorescent polystyrene particles of a size range (1–7 μm) similar to the size of Cryptosporidium oocysts (about 5 μm) without added coagulant was less than 50%. Removal of the particles under the operating conditions above but with the addition of either of the coagulants polyaluminium chloride (PAC) or aluminium sulphate was capable of giving better than 99% removal of the particles.     

BAC滤池对浊度和颗粒数的控制研究

传统的贾第鞭毛虫和隐孢子虫（简称“两虫”）检测方法存在诸多不足，为此选用浊度和颗粒数作为“两虫”的替代指标，以对浊度和颗粒物的去除率来衡量生物活性炭（BAC）滤池对“两虫”的控制效果。试验结果表明：采用颗粒数表征滤后水水质比采用浊度更适宜。过滤初期颗粒数从峰值降到50个／mL以下所需的时间比浊度降到0．1NTU所需的时间多1h左右。正常过滤期间BAC滤池进水浊度一般在0．1NTU以下，经过BAC滤池处理后，浊度得到进一步降低，平均去除率为52．7％。炭层对浊度的去除率为56．4％，其出水浊度基本上都低于0．05NTU，而砂层对浊度不但没有去除能力，反而使出水浊度平均上升了约3．7％。炭层对颗粒物的平均去除率为33．3％，砂层对颗粒物的平均去除率为8．5％。     

Combined use of an electrostatic precipitator and a high‐efficiency particulate air filter in building ventilation systems: Effects on cardiorespiratory health indicators in healthy adults

High‐efficiency particulate air (HEPA) filtration in combination with an electrostatic precipitator (ESP) can be a cost‐effective approach to reducing indoor particulate exposure, but ESPs produce ozone. The health effect of combined ESP‐HEPA filtration has not been examined. We conducted an intervention study in 89 volunteers. At baseline, the air‐handling units of offices and residences for all subjects were comprised of coarse, ESP, and HEPA filtration. During the 5‐week long intervention, the subjects were split into 2 groups, 1 with just the ESP removed and the other with both the ESP and HEPA removed. Each subject was measured for cardiopulmonary risk indicators once at baseline, twice during the intervention, and once 2 weeks after baseline conditions were restored. Measured indoor and outdoor PM_2.5 and ozone concentrations, coupled with time‐activity data, were used to calculate exposures. Removal of HEPA filters increased 24‐hour mean PM_2.5 exposure by 38 (95% CI: 31, 45) μg/m³. Removal of ESPs decreased 24‐hour mean ozone exposure by 2.2 (2.0, 2.5) ppb. No biomarkers were significantly associated with HEPA filter removal. In contrast, ESP removal was associated with a ?16.1% (?21.5%, ?10.4%) change in plasma‐soluble P‐selectin and a ?3.0% (?5.1%, ?0.8%) change in systolic blood pressure, suggesting reduced cardiovascular risks.