Biological Sand Filters Research Articles

Danish guidelines for small-scale constructed wetland systems for onsite treatment of domestic sewage

The Danish Ministry of Environment and Energy has passed new legislation that requires the wastewater from single houses and dwellings in rural areas to be treated adequately before discharge into the aquatic environment. Therefore official guidelines for a number of onsite treatment solutions have been produced. These include guidelines for soakaways, biological sand filters, technical systems as well as different types of constructed wetland systems. This paper summarises briefly the guidelines for horizontal flow constructed wetlands, vertical flow constructed wetlands, and willow systems with no outflow and with soil infiltration. There is still a lack of a compact onsite solution that will fulfil the treatment classes demanding 90% removal of phosphorus. Therefore work is presently being carried out to identify simpler and robust P-removal solutions.

Biodegradation of gasoline compounds (BTEX) in a water works sand filter

Various chemical compounds including aromatic gasoline compounds frequently contaminate drinking water wells in urban areas. Because ground water treatment is simple, usually consisting of aeration/stripping and sand-filtration, it is of significant interest to know the ability of the conventional treatment to remove the chemical contaminants. The removal of gasoline compounds was investigated in a two-stage pilot scale sand filter, each with a filter depth of 0.8–1 m and with a filtration rate of 7.6 m/h. The concentrations of aromatic compounds were in the range 7–15 μg/L, which are realistically low concentrations. The experiments demonstrated a surprisingly high removal efficiency of the filter system. Most of the hydrocarbons were removed already in the primary filter (3 mm sand grains) and the concentrations were in the range 0.05–0.1 μg/L at the outlet from the secondary filter (1 mm sand grains). Influent iron concentrations in the range 0–4 mg/L and backwashing did not adversely affect the biodegradation of hydrocarbons. This study has shown that a conventional biological active sand filter can act as an efficient barrier against gasoline compounds, thereby saving the consumer capital costs and operational costs from installation of supplementary treatment.

Retention and removal of the fish pathogenic bacterium Yersinia ruckeri in biological sand filters.

To investigate the retention and removal of the fish pathogenic bacterium Yersinia ruckeri in biological sand filters and effects on the microbial community composition. Sand filter columns were loaded (70 mm day(-1)) with fish farm wastewater and a suspension (10(8) CFU ml(-1)) of Y. ruckeri. Bacterial numbers and protozoan numbers were determined by plate counts and epifluorescence microscopy, respectively, and microbial biomass and community composition were assessed by phospholipid fatty acids (PLFA) analysis. Concentrations of Y. ruckeri in the filter effluent decreased from 10(8) to 10(3)-10(5) CFU ml(-1) during the experiment. Numbers of Y. ruckeri in the sand decreased from 10(6) CFU g(-1) dry weight (DW) sand to 10(4) CFU g(-1) DW sand. In contrast, microbial biomass determined with plate counts and total PLFA increased during the whole experiment. Principal component analysis (PCA) revealed a change in microbial community composition with time, with the most pronounced change in surface layers and towards the end of the experiment. Protozoan numbers increased from ca 0-600 cells g(-1) DW sand, indicating the establishment of a moderate population of bacterial grazers. The removal of Y. ruckeri improved during the experiment. Introduction of Y. ruckeri to the sand filter columns stimulated growth of other micro-organisms, which in turn caused a shift in the microbial community composition in the sand. This study increases the understanding of the dynamics of sand filters subjected to a high loading of a pathogenic bacterium and can therefore be used in future work were the overall aim is to provide a more reliable and efficient removal of pathogenic bacteria in biological sand filter systems.

Bacterial removal and protozoan grazing in biological sand filters.

The objective of the study was to investigate the importance of protozoan predation as a biological removal mechanism in sand filters used for purification of bacteria from wastewater. Eleven sand filter columns were seeded with a high dose of wastewater (70 mm d(-1)) and a high concentration (10(8) colony forming units [CFU] mL(-1)) of Aeromonas hydrophila (American Type Culture Collection [ATCC] 14715) for a period of 30 d. Water samples from three filter outlets were analyzed for the concentration of A. hydrophila. In addition, one filter column was sacrificed each sampling day for the quantification of A. hydrophila, culturable bacteria (heterotrophic plate counts, HPC), total bacterial counts, and protozoa in the sand. The mean removal efficiency of A. hydrophila in the sand filter columns was 4.7 log units. The concentration of A. hydrophila in the sand filter effluent, however, had a clearly time-dependent pattern from high (log 6) and unstable concentrations to low and more stable levels (log 2). The removal efficiency of A. hydrophila correlated significantly (P = 0.0005, r2 = 0.6) with numbers of protozoa in the sand filters. Significantly higher (P < 0.05) concentrations of A. hydrophila were observed in sand filter effluents from columns treated with the protozoan inhibitor cycloheximide, compared with nontreated columns. Results from the present study show that protozoan grazing plays an important role as a bacterial removal mechanism in sand infiltration systems.

Removal of fish pathogenic bacteria in biological sand filters

Documentation is required to evaluate the use of infiltration systems as an alternative method for removal of fish pathogenic bacteria in wastewater from fish-farms. This study was performed to investigate the removal of bacterial fish pathogens in biological sand filters. A second aim of the study was to evaluate the bacteria used in the study in order to find a suitable model organism for future experiments. Low-strength wastewater from an inland freshwater salmonid farm was intermittently loaded (70 mm/day in 24 doses) to filter columns containing either fine sand ( d 10=0.25) or coarse sand ( d 10=0.86). After a wastewater loading period of 10 weeks, separate sand columns were seeded with Yersinia ruckeri, Pseudomonas fluorescens, Aeromonas hydrophila and Aeromonas salmonicida subsp. salmonicida, respectively, for a period of 30 days. All the bacteria showed the same removal performance during the experiment, with a significantly lower removal in the beginning of the experiment (day 1–7) compared to mid- and late-phase (day 12–30). In mid- and late-phase the removal stabilized at a high level (>99.9%) for all the bacteria. The hydrophobic cell surface properties of the Aeromonads were higher than Ps. fluorescens and Y. ruckeri. This can possibly explain the significantly higher ( P<0.05) removal efficiencies seen for A. hydrophila and A. salmonicida subsp. s almonicida compared to Y. ruckeri and Ps. fluorescens. Results were promising with regard to the use of low-cost infiltration systems as an alternative disinfection method for fish-farm wastewater. Following the criteria for a suitable model organism (removal efficiency, detection in filter effluent and die-off in storage tanks), Y. ruckeri was found to be a feasible model organism for use in future experiments.

Evaluation of Small Wastewater Treatment Plants in the County of Århus – Denmark

Influent and effluent data from about 120 small wastewater treatment plants (100 - 2000 PE) have been collected and processed. Seven different types of plants are represented. The effluent quality and the treatment efficiency have been evaluated. The most common type of plant is mechanical/biological treatment plants. Some of them are nitrifying and some are also extended for chemical precipitation of phosphorus. Constructed wetlands and biological sandfilters are also represented among the small wastewater treatment plants.

Purification Efficiency of Danish Biological Sand Filter Systems

During an investigation in 1989 on small low technology treatment systems, particularly reed bed and biological sand filter systems in Denmark, it appeared that biological sand filter systems offer several advantages for the treatment of small wastewater sources. These observations gave rise to a new project concerning systematic registration of all biological sand filter systems in Denmark. Besides this registration the aim of the project was to indicate the reliability of these systems concerning removal ability and to give some general guidelines on different circumstances which seem to have positive or negative effects on the removal of particularly ammonium and phosphorus. The paper summarizes the results and experiences that have been collected since the beginning of the use of biological sand filter systems in Denmark in the late 70s. Typical purification efficiencies of 90-95% for BI5, 30-45% for nitrogen and 40-60% for phosphorus were observed. The ripening of sand filters to their maximum removal capacity is often short, within a few months, but longer periods of about 6 months may be required to achieve full nitrification. High nitrogen removal depends on the nitrification processes and also of anoxic zones in the filter with denitrification. The best way to achieve good nitrification is to use coarse-grained sand. The removal of phosphorus is indeed affected by the chemical properties of the sand in question. In ferrous enriched sand it is possible to achieve removal efficiencies of 70-90% of the phosphorus at concentrations of 10-15 mg P/l in the inlet.

Recovery of water and auxiliary chemicals from effluents of textile dye houses

A process to recover at least 80% of water, auxiliary chemicals and energy from effluents of textile dye-houses has been developed. The water and the auxiliary chemicals can be reused by the textile industry to dye either light or dark shades. Energy is recovered in the form of hot water. The pay-back time for the process is between 18 and 30 months, depending upon the degree of automation. Moreover, this technology minimizes the discharge of pullutants contributing greatly to the solution of many environmental problems. Spiral wound membrane modules specifically designed for this application are used. Pretreatment to the membrane system is done by physico-chemical and/or biological units and sand filters.

FILTRATION TECHNIQUE FOR RECIRCULATING AQUACULTURE SYSTEMS

ABSTRACTThe use of biological filters in closed systems to maintain salmonids and crustaceans is becoming more common as commercial aquaculture ventures approach the urban marketplace. Competition for land and water resources makes the capital costs for equipment, tanks, and material economically feasible. The advantages of intensive closed system aquaculture are greater control over water quality, more production per unit area, and controllable growth rates. The feeding techniques and high loadings generally produce a concentrated wastewater that must be treated by physical, chemical, and biological processes before reuse. Treatment of ammonia, nitrite, and suspended solids are the primary concerns of the culturist. This paper describes the removal efficiencies of biological sand filters in commercial service for various loading parameters. Design factors and the ranges of operation for different systems and organisms are related to data collected over two years of culture. Particular attention is paid to the various soluble and solid forms of nitrogenous waste and their removal in prefiltration, submerged, and trickling biological oxidation systems. The recycled water is returned to many different tanks for polyculture production of fish and crustaceans.

The Fate of Some Metal Species: Lead, Cadmium, Zinc in Surface Water, during Biological Sand Filtration – Effect of Preozonation

This study was performed to determine the elimination of the different chemical species of some toxic metals - zinc, lead, cadmium - during biological sand filtration on surface water containing humic material which is able to promote the complexation of metals. The effect of preozonation was examined. The metal speciation was realised by means of Atomic Absorption Spectrometry and Differential Pulse Anodic Stripping Voltammetry. The survey of organic matters was carried out by measuring TOC, UV absorption and fluorescence. The biological treatment of raw water is quite effective for the removal of particu-late metals. The data bring out an important decrease for dissolved metals - about 50 to 60 % with cadmium and lead - especially noteworthy for the labile complexed metals. The preozonation of raw water provides the redissolution of particulate cadmium and zinc which are converted to free metals and seem then to be more eliminated by biological filtration. Ozonation appears to improve the efficiency of biological treatment which usually gives higher yields of purification than floculation (aluminium sulfate) in the same conditions.