Limestone Filter Research Articles

Use of calcium carbonate as a wet contact filter

The groundwaters in Finland are usually acidic and soft. In fact, the most common quality factor necessitating water treatment procedures in Finland is the acidity of water. Following this come excessive levels of iron or manganese. Biological methods, such as a combination of dry filtration and slow sand filtration, are commonly used to remove iron and manganese and raise pH. Several advantages can be gained by using limestone filtration to replace the dry filter at the beginning of the process, and as alkalising wet filtration before the slow sand filter. Limestone wet filtration can be combined with aeration, if necessary. This research investigated the suitability of combined alkalising wet filtration and slow sand filtration for the treatment of water from the Monttu water supply plant in Liminka, Finland. It was studied through a series of both short-term filtration tests and long-term pilot tests. Alkalising wet filtration combined with slow filtration proved to work well with this water. The treatment reduced the iron content from 3·5 mg/l to 0·05 mg/l and the manganese content from 0·09 mg/l to < 0·01 mg/l. The pH of the raw water was 6·2, and that of the treated water was 7·5.

Use of calcium carbonate as a wet contact filter

The groundwaters in Finland are usually acidic and soft. In fact, the most common quality factor necessitating water treatment procedures in Finland is the acidity of water. Following this come excessive levels of iron or manganese. Biological methods, such as a combination of dry filtration and slow sand filtration, are commonly used to remove iron and manganese and raise pH. Several advantages can be gained by using limestone filtration to replace the dry filter at the beginning of the process, and as alkalising wet filtration before the slow sand filter. Limestone wet filtration can be combined with aeration, if necessary. This research investigated the suitability of combined alkalising wet filtration and slow sand filtration for the treatment of water from the Monttu water supply plant in Liminka, Finland. It was studied through a series of both short-term filtration tests and long-term pilot tests. Alkalising wet filtration combined with slow filtration proved to work well with this water. The treatment reduced the iron content from 3·5 mg/l to 0·05 mg/l and the manganese content from 0·09 mg/l to < 0·01 mg/l. The pH of the raw water was 6·2, and that of the treated water was 7·5.

Removal of copper from water using limestone filtration technique: determination of mechanism of removal

This paper discusses heavy metal removal from wastewater by batch study and filtration technique through low-cost coarse media. Batch study has indicated that more than 90% copper (Cu) with concentration up to 50 mg/l could be removed from the solution with limestone quantity above 20 ml (equivalent to 56 g), which indicates the importance of limestone media in the removal process. This indicates that the removal of Cu is influenced by the media and not solely by the pH. Batch experiments using limestone and activated carbon indicate that both limestone and activated carbon had similar metal-removal efficiency (about 95%). Results of the laboratory-scale filtration technique using limestone particles indicated that above 90% removal of Cu was achieved at retention time of 2.31 h, surface-loading rate of 4.07 m 3/m 2 per day and Cu loading of 0.02 kg/m 3 per day. Analyses of the limestone media after filtration indicated that adsorption and absorption processes were among the mechanisms involved in the removal processes. This study indicated that limestone can be used as an alternative to replace activated carbon.

Combination of membrane technology and limestone filtration to control drinking water quality

Certain areas in Finland have a problem of high fluoride and aluminium in groundwater because of soil properties. In 1999, the City of Laitila constructed a membrane filtration plant (16–25m 3/h) to control fluoride and aluminium concentration in drinking water. The plant has two trains, one with reverse osmosis (RO) and the other with nanofiltration (NF). Only a fraction (ca. 1/4) of water distributed is membrane filtered. The rest flows directly to alkalization. The alkalization process includes two limestone filters: one for membrane-filtered water (RO+NF) and the other for untreated groundwater. During the first year of operation, both RO and NF were shown applicable for fluoride removal from soft, high fluoride (ca. 4 mgF/l) ground water. The fluoride removals were on average > 95% in RO at 7.3 bar and 76% in NF at 5.7 bar. More than 78% of aluminium was also removed in membrane filtration. Temperature (2–16°C) affected permeated conductivities in the NF unit but not in the RO unit. Limestone filtration was shown applicable for alkalization of membrane filtered water. The alkalinity of membrane-filtered water rose back to the level it was before membrane filtration. However, alkalinity achieved with membrane-filtered water was lower than with groundwater while pH obtained was higher. This mainly resulted from the difference in carbon dioxide concentration of these waters. Since start-up of the RO/NF plant, fluoride and aluminium concentrations in the water distribution system have been at acceptable levels (≤1.5 mgF/l, ≤0.2 mgAl/l) while limestone filtration has ensured a stable alkalinity and pH. The cost of membrane filtration was ca. Euro 0.2/m 3 permeate.

Treatment of soft reservoir water by limestone filtration in combination with ultrafiltration

Treating surface waters from reservoirs usually means the removal of manganese and particles as well as the adjustment of pH to reach calcium carbonate equilibrium. A new combination of limestone filtration and ultrafiltration (UF) was investigated in pilot experiments. Results on particle and manganese removal efficiency and specific permeate flux dependence on backwash procedure are discussed and aspects for further research are shown. The full-scale concept of a new water work based on the pilot experiments is presented. Costs are discussed for the comparison of membrane technology to conventional direct filtration.

Nanofiltration in Combination with Limestone Filtration for Treating a Soft Spring Water Containing High Amounts of Humic Substances

AbstractThe paper presented here describes experiments with a nanofiltration pilot plant treating spring water which contains high amounts of humic substances. With this process, water components such as humic substances, iron, manganese, and aluminum may be very well removed. However, the low pH value of the NF filtrate does not conform with the German standards. This is why the pH value will be increased in a second treatment step by limestone filtration. Prior to limestone filtration, CO2 dosage is required in order to make sure that the pH value stays below the upper limit of the German standards of 9.5. With this treatment, a drinking water results which meets the German standards and has good chemical properties with respect to corrosion.The operation of the nanofiltration pilot plant for the treatment of the very soft spring water did not require the continuous addition of chemicals in order to prevent scaling. Although the spring water entered the NF without chemical pretreatment, there was no decrease in filtrate capacity observed over a period of six months. This is in contrast to other investigations involving colour reduction from very hard surface waters. When treating very hard waters by nanofiltration, the addition of complexing agents or acid is required in order to prevent scaling of the membranes. Such intricate pretreatment procedures cause doubt of the application of nanofiltration for the treatment of hard waters in large plants. However, in the case presented here, the application of NF in combination with the hardening step is quite simple, so that the full‐scale plant may be operated mainly automatically and will require only little maintenance.

The Use of Limestone Bed Filtration for the Treatment of Ferruginous Groundwater

AbstractA pilot plant, consisting of limestone bed and sand filtration units, has been built 15 km south of Cairo to serve about 400 people. The plant comprises three limestone filter units (operated in series) and two sand filters.Operation of the pilot plant has shown that a packed limestone filter unit is a simple and cheap method of removing iron from ferruginous groundwater. The results demonstrate an iron removal rate of about 60% after passing through one 1.15−m deep limestone filter operating with a surface loading rate up to 1.4 m3/m2. h. The overall iron removal after one limestone filter followed by sand filtration was more than 90%.

Reduction in the toxicity of boiler blowdown effluent by addition of calcium or humic acid

AbstractBoiler blowdown effluent from both nuclear and thermal electric generating stations was frequently toxic to both rainbow trout and Daphnia magna in monitoring tests. The toxicity could be caused either by the low ionic content of the effluent, or through interactions of the low ionic content and elevated metal concentrations. Followup studies were conducted to characterize the toxicity of the effluent and develop methods to reduce its toxicity. Addition of calcium, either by adding calcium chloride (CaCl2) or recirculating the effluent over a limestone filter for ∼ 12 h, largely eliminated the toxicity of boiler blowdown effluent to trout; however, the treated effluent remained toxic to D. magna. Adding humic acid (∼ 20 mg L−1 as dissolved organic carbon) significantly reduced the toxicity of boiler blowdown effluent to both D. magna and rainbow trout. The toxicity of boiler blowdown effluent appears to result from the interactions of its low ionic content and elevated metal concentrations, but ad...

A Study into the Removal of Iron from Ferruginous Ground Water Using Limestone Bed Filtration

A pilot plant consisting of limestone bed filtration and sand filtration has been built 15 km south of Cairo to serve about 400 people. The pilot plant consists of 3 limestone filter units operated in series and two sand filters. The limestone filters are 1.3 m × 1.3 m and have a media depth of 1.15 m, a liquid depth of 0.5 m plus 0.35 m free board. The pilot plant started operation in April 1991 and the initial operation of the pilot plant has shown that a packed limestone filter unit is a simple and cheap method of removing iron from ferruginous groundwater. The initial results have shown that when an inlet water of about 5 mg/l of iron is treated by one limestone filter and one sand filter at a flow rate of 0.9 m3/h, the treated water had an average iron concentration of 0.2 mg/l.

Remineralization of desalinated water by limestone dissolution filter

Remineralization by the limestone process is now widely used in the post-treatment sections of MSF desalination plants and RO plants. This paper discusses the optimization of the process design based on our experiments, process simulation and the data obtained from actual plant operation. The following aspects were considered. • - evaluation of limestone dissolution kinetics. • - design parameters of limestone filter bed, such as LHSV, particle size, CO 2 concentration, etc. • - effect of backwashing • - CO 2 availability from MSFE venting system. • - residual CO 2 desorption before a alkali dosing, etc. Through this study, the residual CO 2 desorption process by a simple air bubble column has been developed. With the application of this process, alkali consumption for pH adjustment is remarkably reduced and a high by-pass ratio of limestone filter (about 70%) can be realized. This process will contribute to reduce not only the variable cost, but the fixed cost of a remineralization plant.

LIMING OF A FINAL CUT ACID LAKE

ABSTRACT One part of an overall reclamation project for an abandoned strip mine area included neutralizing an acid lake. Other portions of the project included neutralizing acid mine drainage from spoil banks and coal refuse areas in the areas adjacent to the lake. The overall reclamation plan included clay cover, soil amendments, vegetation for all project areas, drainage through a limestone filter to the lake, and neutralization of the acid lake. Laboratory neutralization studies indicated >90,000 kg of lime would be required to neutralize the 4-ha lake which had pH of 2.7 and acidity of 850 mg L−1. Field tests prior to actual liming operations indicated the acidity in the lake had been reduced 50 percent; therefore, liming requirements were reduced correspondingly. The lime was applied by mixing a lime slurry in a hydroseeder apparatus and spraying onto the surface of the lake. The pH values increased form 2.8 to 3.2. One month later a second application of hydrated lime was applied in a similar fashion and pH changed from 3.2 to 3.6 with reduced acidity. Additional laboratory neutralization studies were performed in November 1984; another application of lime increased the lake water pH to 4.8. Results of additional samples collected during August 1985 indicated pH at 6.5, reduced transparency, and chlorophyll a values appearing for the first time.