Biomass development in slow sand filters

Microbial biomass development in the sand and schmutzdecke layer was determined in two full-scale slow sand filters, operated with and without a light excluding cover. A standard chloroform fumigation-extraction technique was adapted to routinely measure microbial biomass concentrations in the sand beds. Sand was sampled to a depth of 10 cm and schmutzdecke was also collected at the same random positions on the uncovered filter. Interstitial microbial biomass in the uncovered sand bed increased with time and decreased with sampling depth. There was a small accumulation of sand biomass with time in the covered filter, but no relationship was apparent between biomass concentration and depth in this filter. Schmutzdecke did not develop on the covered filter and was spatially highly variable in the uncovered condition compared to the consistent patterns observed in interstitial biomass production. It is speculated that microbial biomass in the sand of uncovered filters is largely related to carbon inputs from photosynthetic activity in the schmutzdecke and involves mechanisms that spatially distribute carbon substrate from the schmutzdecke to the sand. However, total organic carbon and dissolved organic carbon removals were similar in both filters suggesting that relatively small biomass populations in covered filters are sufficient to remove residual labile carbon during advanced water treatment and little further advantage to water purification and organic carbon removal is gained by the increased production of biomass in uncovered slow sand filter beds.     

Environmental aspects of the use of NTA as a detergent builder

The behaviour, fate and significance of the detergent builder nitrilotriacetic acid (NTA) has been reviewed with particular reference to the removal of NTA during wastewater treatment and the effects of NTA on heavy metal solubility both during treatment and in the receiving environment. It is concluded that NTA removal during secondary biological treatment is subject to considerable variation, both temporal and between works as a result of changes in NTA load, temperature, water hardness and treatment process parameters. As a result of such variability, effluent NTA concentrations may be sufficient to mobilise heavy metals resulting in metal contamination of receiving waters and potable waters, particularly in areas of low effluent dilution and high water re-use. Removal of NTA during primary sedimentation and septic tank treatment is concluded to be predominantly due to adsorption to the sludge solids while removal in anaerobic sludge digestion is subject to operational characteristics of the treatment works. Disposal of NTA contaminated sludge to land may contaminate groundwaters and affect heavy metal speciation, while the disposal of contaminated sludge or sewage to sea may result in toxic algal blooms, in addition to effects on metal speciation.     

Efficiency of industrial minerals on the removal of mercury species from liquid effluents

Increasing attention has been given, by the industrial sector, to the removal of heavy metals from liquid effluents to satisfy environmental regulations. For this purpose, the most common methods utilized include: chemical precipitation, cementation, ion exchange, adsorption and solvent extraction. All these methods have limitations such as slow kinetics, low adsorption capacity and they are usually very expensive. Thus, new technologies for heavy metal removal are of great interest. This study consisted on a screening of industrial minerals to check their efficiencies to remove mercury from liquid effluents. The methodology employed a batch adsorption technique. The tested minerals included: atapulgites, zeolites, magnetites, kaolin, vermiculite and bentonite. Results show relatively high efficiencies of magnetite and zeolite on mercury removal. These minerals were capable to remove mercury species from effluents with concentrations reaching 1,000 ppm, corresponding to a sorption capacity of 10,000 mg Hg/kg. The sorption maximum was not reached in these tests. In addition, it became evident the importance of mercury speciation at the solid:liquid interface, with relevant consequences on the application of this technology to effluent treatment.     

Residual heavy metal removal by an algae-intermittent sand filtration system

A laboratory scale study was undertaken to determine the feasibility of using algae growing in wastewater lagoons to absorb residual heavy metals for subsequent complete removal by intermittent sand filtration of the metal laden algae. In semi-continuous cultures the mixed algal flora native to wastewater lagoons absorbed 70–90% of the cadmium and copper from the wastewater media. Chromium absorption was less by ratio (20% was absorbed), but the mass of chromium removed was much greater as high levels of chromium were added. Only one alga (Oscillatoria sp.) which was extremely resistant to chromium grew in the chromium exposed cultures. Nearly total removal of the cadmium and copper was achieved by the algae-intermittent sand filter system. The net chromium removal agreed with the accumulation analyses.The technical feasibility of removing certain heavy metals from wastewater with such a system was established. However, in depth laboratory and field studies must be conducted to maximize system efficiency, demonstrate tactical limitations, and establish design specifications.     

Treatment of oil well “produced water” by waste stabilization ponds: Removal of heavy metals

Oil well produced water (PW) can serve as an alternative water resource for restricted halotolerant agricultural purposes if the main pollutants, hydrocarbons and heavy metals, can be removed to below the irrigation standards. In this work, the potential removal of cadmium(II), chromium(III) and nickel(II) from PW by chemical precipitation in biological treatment was evaluated. Precipitation as a sulphide salt was found to be a very effective mechanism, which together with biosorption, biological metal uptake, precipitation as hydroxides and carbonates could remove heavy metals down to below irrigation standards. The existence and capability of these various mechanisms was demonstrated in the performance of a continuous artificial pond followed by intermittent sand filter, achieving removals of around 95% for nickel(II) and even higher removal rates for cadmium(II), chromium(III) from artificial PW after the installation of an anaerobic stage. The treated effluent quality was higher than that required by current European standards.     

Simultaneous removal of As, Cd, Cr, Cu, Ni and Zn from stormwater: experimental comparison of 11 different sorbents

The potential of using alumina, activated bauxsol-coated sand (ABCS), bark, bauxsol-coated sand (BCS), fly ash (FA), granulated activated carbon (GAC), granulated ferric hydroxide (GFH), iron oxide-coated sand (IOCS), natural zeolite (NZ), sand, and spinel (MgAl(2)O(4)) as sorbents for removing heavy metals from stormwater are investigated in the present study. The ability of the sorbents to remove a mixture of As, Cd, Cr, Cu, Ni and Zn from synthetic stormwater samples were evaluated in batch tests at a starting pH of 6.5. The metal speciation and saturation data is obtained using the PHREEQ-C geochemical model and used to elucidate the sorption data. It is found that BCS, FA, and spinel have significantly higher affinity towards heavy metals mainly present as cationic or non-charged species (i.e. Cd, Cu, Ni and Zn) compared to those present as anionic species (i.e. As and Cr). However, IOCS, NZ and sand have higher affinity towards As and Cr, while alumina has equally high affinity to all tested heavy metals. The Freundlich isotherm model is found to fit the data in many cases, but ill fitted results are also observed, especially for FA, BCS and GAC, possibly due to leaching of some metals from the sorbents (i.e. for FA) and oversaturated conditions making precipitation the dominant removal mechanism over sorption in batches with high heavy metal concentrations and pH. Calculated sorption constants (i.e. K(d)) are used to compare the overall heavy metal removal efficiency of the sorbents, which in a decreasing order are found to be: alumina, BCS, GFH, FA, GAC, spinel, ABCS, IOCS, NZ, bark, and sand. These findings are significant for future development of secondary filters for removal of dissolved heavy metals from stormwater runoff under realistic competitive conditions in terms of initial heavy metal concentrations, pH and ionic strength.     

The role of aluminum in slow sand filtration

Engineering enhancement of slow sand filtration has been an enigma in large part because the mechanisms responsible for particle removal have not been well characterized. The presumed role of biological processes in the filter ripening process nearly precluded the possibility of enhancing filter performance since interventions to enhance biological activity would have required decreasing the quality of the influent water. In previous work, we documented that an acid soluble polymer controls filter performance. The new understanding that particle removal is controlled in large part by physical chemical mechanisms has expanded the possibilities of engineering slow sand filter performance. Herein, we explore the role of naturally occurring aluminum as a ripening agent for slow sand filters and the possibility of using a low dose of alum to improve filter performance or to ripen slow sand filters.     

Heavy metals in rivers of Latvia

Total heavy metal concentrations in waters and sediments (HNO3 digestible Pb, Cu, Co, Ni, Mn, Zn) and their speciation forms in sediments (exchangeable, carbonate bound, iron-manganese oxide bound, organic matter bound and residual) in major and common small watercourses (31 sampling stations) along their flow in Latvia were determined. The metal loads entering the Baltic Sea from Latvia were calculated. Increased metal concentrations were found only in lower reaches of the largest rivers and locally around known industrial pollution sources. Differences in metal concentrations and loads in rivers from different regions of Latvia were related to natural geochemical processes. Metal speciation analysis showed that the dominant metal species are residual metals and those bound to organic matter. Residual and carbonate-bound metal dominated only in rhitral regions of rivers. The concentrations of exchangeable metals increased below pollution sources.     

天然有机物对改性滤料除锰效能的影响

腐殖质与铁、锰形成的络舍物吸附在滤料表面后有可能降低滤池的除锰效果，为此通过试验考察了天然有机物（NOM）对改性滤料接触氧化过滤工艺除锰效能的影响。结果表明，该工艺的除锰效果极佳，但天然有机物的存在会使除锰效率及过滤周期大幅度降低，而预投氯可保证改性滤料对锰的高效去除。有机物含量和投氯量对除锰效果有直接影响，应结合原水水质确定最佳投氯量。     

Modeling antimicrobial contaminant removal in slow sand filtration

Slow sand filters are used in rural regions where source water may be subjected to antimicrobial contaminant loads from waste discharges and diffuse pollution. A numerical model (LETA) was derived to calculate aqueous antimicrobial concentrations through time and depth of a slow sand filter and estimate accumulating contaminant mass in the schmutzdecke. Input parameters include water quality variables easily quantified by water system personnel and published adsorption, partitioning, and degradation coefficients. Simulation results for the tetracycline, quinolone, and macrolide classes of antimicrobials suggested greater than 3-log removal from 1 microg/L influent concentrations within the top 40 cm of the sand column, with schmutzdecke antimicrobial concentrations comparable to other land-applied waste biosolids. A 60-day challenge experiment injecting 1 microg/L tylosin to a pilot slow sand filter showed an average 0.1mg/kg of the antimicrobial remaining in the schmutzdecke layer normally removed during filter maintenance, and this value was the same order of magnitude as the sorbed concentration predicted by the LETA model.     

Coregionalization analysis of heavy metals in the surface soil of Inner Mongolia

Due to potential problems associated with their deficiencies or toxicities, heavy metals in soils are of great environmental concern. To evaluate heavy metal contents and their relationships in the surface soil of Inner Mongolia, soil samples were collected from 344 sites and contents of copper, lead, zinc, cadmium, nickel, chromium, mercury, cobalt, vanadium and manganese were determined. In this article, coregionalization of these ten heavy metals is investigated using factorial kriging. Vegetation type, parent material type and soil pH, with respective characteristic ranges of 200, 400 and over 1000 km, are identified as the primary factors that control the spatial distribution of soil heavy metals. At the scale of 200 km, heavy metal relationships mainly reflect the result of biocycling. Their relationships at the intermediate scale (400 km) are thought to be derived from the atomic substitution of metals in the parent materials. Effects of soil pH on the adsorption of heavy metals by soil organic materials could explain their relationships at the large spatial scale (over 1000 km).     

Simultaneous removal of Cu, Mn and Zn from drinking water with the use of clinoptilolite and its Fe-modified form

Zeolites have been widely used in water treatment and especially clinoptilolite, due to its low cost and high abundance. It has large cation-exchange capacity and is capable of removing large quantities of heavy metals from contaminated water samples. By loading the surface of clinoptilolite with amorphous Fe-oxide species, a total improvement in adsorption capacity could be achieved. Thus, the Clin–Fe oxide system is capable of adsorbing significantly higher heavy metal concentrations than untreated clinoptilolite with simultaneous noticeable decrease in water hardness. Batch adsorption experiments have shown that Clin–Fe system has very large Cu, Zn and Mn adsorption capacity and for most of the cases the treated water samples were suitable for human consumption or agricultural use. New experiments were conducted to study the effectiveness of clinoptilolite and of the Clin–Fe system in removal of Cu, Mn, Zn, present simultaneously in water samples, so that the study of metal–sorbent chemical behavior and of the adsorption selectivity would be feasible. Desorption of metals was also examined and an integrated approach of the effectiveness of such materials in drinking water treatment is presented.     

Removal of biodegradable dissolved organic carbon in a water treatment plant

A new scheme of treatment has been developed in the water treatment plant of Ivry-sur-Seine near Paris. This treatment consists of a pretreatment of preozonization, contact coagulation, coagulation on a filter, slow sand filtration, ozonization and GAC filtration. We have tested the efficiency of this new line of treatment for the removal of BDOC and have attempted to correlate the results with the removal of organic matter (global parameters). Results show a very good efficiency of slow sand filtration and we think that this treatment step allows production of a biologically stable water.     

无机固形物对重金属的吸附去除特性研究

采用石英砂和高岭土为吸附剂,以典型重金属Cu,Zn,As,Cr为吸附质分别进行了单吸附剂单吸附质等温吸附实验,研究了无机颗粒物对重金属离子的吸附去除特性以及无机颗粒物对金属离子吸附水相化学条件影响因素,得出了一些有参考价值的结论。     

Speciation (including adsorbed species) of copper, lead, nickel and zinc in the Meuse River: Observed results compared to values calculated with a chemical equilibrium computer program

The adsorption of trace metals on sediments of the Meuse River was interpreted in terms of competition between metals and protons for surface sites. Surface constants (^*β₁^surf) were determined for Cu, Zn and Cd (10^−1.8, 10^−3.6 and 10^−3.7). The constants for Pb, Ni, Ca and Mg (10^−1.7, 10^−3.8, 10^−6.5 and 10^−5.2) were estimated using a correlation between hydrolysis and surface constants. A chemical equilibrium computer program in which surface sites (for adsorption reactions) are treated as conventional ligands was used to calculate the speciation of Cu, Pb, Ni and Zn in the Meuse River. Calculated values of the adsorbed/dissolved distribution agreed well with observed values, after some realistic data manipulation. This work indicates that dissolved trace metal concentrations in the Meuse River are controlled by adsorption and not by precipitation mechanisms. The relationship between organic matter and suspended matter greatly influences the adsorption of metals like Cu and Pb.     

DBPs removal in GAC filter-adsorber

A rapid sand filter and granular activated carbon filter-adsorber (GAC FA) were compared in terms of dissolved organic carbon (DOC) and disinfection by-products (DBPs) removal. A water treatment plant (WTP) that had a high ammonia concentration and DOC in raw water, which, in turn, led to a high concentration of DBPs because of a high dose of pre-chlorination, was investigated. To remove DBPs and DOC simultaneously, a conventional rapid sand filter had been retrofitted to a GAC FA at the Buyeo WTP in Korea. The overall removal efficiency of DBPs and DOC was higher in the GAC FA than in the sand filter, as expected. Breakthrough of trihalomethanes (THMs) was noticed after 3 months of GAC FA operation, and then removal of THMs was minimal (<10%). On the other hand, the removal efficiency of five haloacetic acids (HAA(5)) in the GAC FA was better than that of THMs, though adsorption of HAA(5) decreased rapidly after 3.5 months of GAC FA operation. And then, gradual improvement (>90%) in HAA(5) removal efficiency was again observed, which could be attributed to biodegradation. At the early stage of GAC FA operation, HAA(5) removal was largely due to physical adsorption, but later on biodegradation appeared to prevail. Biodegradation of HAA(5) was significantly influenced by water temperature. Similar turbidity removal was noticed in both filters, while better manganese removal was confirmed in the sand filter rather than in the GAC FA.     

KDF55/椰壳活性炭/石英砂/沸石联用净化饮用水

考察了KDF55、石英砂、沸石、椰壳活性炭联用对饮用水的净化效果.结果表明,系统对浊度的去除主要发生在椰壳活性炭滤层;对铜、铬、铅等重金属离子的去除主要由KDF55滤层完成,去除率均可达80%以上;系统还可明显降低饮用水的硬度和CODMn.该系统在有效去除污染物的同时,又可向水中释放微量对人体有益的锌离子,对家用净水机的开发具有重要的参考价值.     

Study of pyrene biodegradation capacity in two types of solid media

Removal of pyrene, a representative PAH, was studied using laboratory tests in two different types of solid media: an organic matter collected on the surface of a vertical flow constructed wetland (VFCW) and a formulated clay silicate sand (inorganic matter). The aim of this study was to evaluate the capacity of pyrene biodegradation in these media in order to use them for treating run-off water. The sorption process, the kinetics of pyrene biodegradation and the influence of selected bacteria were also investigated. The sorption process was evaluated by adsorption isotherms and desorption kinetics using a batch equilibration method. The adsorption coefficient values of 28.8 and 2.1 for the organic and the inorganic matter respectively, confirmed the relationship of adsorption with organic carbon content. A small proportion of the sorbed pyrene was available for desorption (8% and 15% for the organic and the inorganic matter, respectively), indicating that sorption was partially irreversible, with the presence of hysteresis. For the formulated clay silicate sand inoculated with a specific bacteria (Mycobacterium sp.6PY1), selected for its ability to degrade PAHs, pyrene removal was complete in 32 days. With the organic matter, these values ranged from 40% to 95% for the different experiments, following a lag time of 3 weeks before observation of a significant degradation. Indigenous bacterial species in the organic medium had the metabolic capacity to degrade pyrene, and microbial populations pre-exposed to the PAH degraded pyrene faster than similar unexposed populations. Three metabolites of pyrene degradation by Mycobacterium were found. They accumulated in both organic and inorganic matter, indicating that the enzymes catalyzing them have slow kinetics.     

Removal and accumulation of Cu, Ni and Zn in horizontal subsurface flow constructed wetlands: Contribution of vegetation and filling medium

This study investigated the accumulation and removal of Cu, Ni and Zn in two horizontal subsurface flow constructed wetlands for domestic wastewater treatment, which differ by shape, presence of macrophytes and water depth. Between March and December 2007, the three metals were measured in the influent and effluents of the two systems. Average percentage removal rates were extremely low for Cu (3% and 9% in the two beds) and higher for Zn and Ni (between 25 and 35%). Under higher Zn influent concentrations, it was found to be between 78-87%, which is in agreement with other literature data.During the peak standing crop season (August), biomasses of the different parts of Phragmites australis (stems, leaves and flowers, roots and rhizomes) were analysed in terms of weight and heavy metal concentration in order to assess heavy metal distribution among the tissues. It was found that the plants contribute to total heavy metal removal to a lesser extent than the filling medium. Aboveground tissues remove 34% of Cu, 1.8% of Ni and 6.2% of Zn % and, once harvested, their disposal does not appear to pose a problem for the environment. If heavy metals are present at high concentrations in the horizontal subsurface flow bed influent, over time, their accumulation in the filling medium could necessitate special care in the bed's management to avoid release into the surrounding environment.     

Desorption characteristics of Cr(III), Mn(II), and Ni(II) in contaminated soil using citric acid and citric acid-containing wastewater

Heavy metal-contaminated soil and wastewater have been attracting an increasing amount of attention due to the potential threat to the surrounding environment and human health. Thus, in this study, citric acid (CA) and citric acid-containing wastewater (CACW) were selected for an evaluation of the influence of the contamination level of the soil, the concentration of citric acid, the contact time, the soil pH, and the ionic interaction on the desorption characteristics of three heavy metals (i.e., Cr(III), Mn(II), and Ni(II)). According to the experimental results, a high concentration of citric acid, an acidic condition, a low level of contamination, and a lengthy contact time were found to be beneficial for desorbing the heavy metals from the contaminated soil. Based on the experimental and calculated results, the H⁺ ions and organic ligands made substantial contributions to the release and adsorption of the heavy metals. The metal ions on the low selectivity sorption sites were leached out earlier than those on the high selectivity sorption sites. The removal percentages of Cr(III), Mn(II), and Ni(II) using CA with a contact time of 6?h were 39.9%, 77.0%, and 62.8%, respectively. By using the CACW as a desorbent, the removal percentages of Cr(III), Mn(II), and Ni(II) with a contact time of 6?h reached 21.4%, 26.9%, and 63.4%, respectively. This suggests a promising practical application of CACW for removing heavy metals from contaminated soil.