Surface Clogging Research Articles

Assessment of Clogging Dynamics in Permeable Pavement Systems with Time Domain Reflectometers

Infiltration is a primary functional mechanism in green infrastructure storm water controls. This study used time domain reflectometers (TDRs) to measure spatial infiltration and assess clogging dynamics of permeable pavement systems in Edison, New Jersey, and Louisville, Kentucky. In 2009, the U.S. Environmental Protection Agency constructed a 0.4-ha parking lot surfaced with three permeable pavement types (permeable interlocking concrete pavers, pervious concrete, and porous asphalt). Paired TDRs were installed at two locations in each permeable pavement type and at a depth of 0.4 m below the driving surface. The relative volumetric water content (RVWC) prior to an event had a significant negative correlation to antecedent dry period, and the peak RVWC during an event had a significant positive correlation to the peak 5-min rainfall intensity. The TDRs measured a significantly different response when water was presumably infiltrating as direct rainfall compared to rainfall combined with runoff from a contributing drainage area. The results indicated clogging progressed from the upgradient edge. Based on the lessons learned at Edison, TDRs were installed in permeable pavement strips in Louisville, Kentucky, during December 2011. The TDR placement strategy was selected to understand the spatial infiltration of runoff and to document clogging and infiltration dynamics. As contributing drainage area size and condition impacts incoming sediment load, and the runoff infiltrates along the upgradient edge of the permeable pavement surface, the ratio of drainage area to working width of permeable surface is an important design parameter to predict the rate of clogging. At Edison, the design ratio of contributing drainage area to permeable pavement width at the upgradient edge was 7.62 m2/m. In Louisville, the ratio was about 3,829 m2/m. Because of the much larger ratio, clogging was expected to occur rapidly at the Louisville site. Responses from rainfall events during the first three months at Louisville supports the hypotheses related to surface clogging mechanisms. This paper highlights evaluation techniques, placement locations, and techniques to use TDRs to remotely monitor surface clogging, which can be used to provide guidance for maintenance scheduling.

Reproductive biology of Stomatium bolusiae (Aizoaceae: Ruschioideae)

Flowers of Stomatium bolusiae are self-incompatible. The species exhibits crepuscular and nocturnal anthesis, exploiting two different pollination mechanisms. The structure of the hermaphroditic flower appears not to favour cross-pollination. The stigmata are never exposed to pollinating agents, which gain access to the floral rewards by forcing their way between the anthers. Clogging of the stigmatic surfaces by self-pollen is common. Nocturnal anthesis, concomitant with the nocturnal release of attractants and the offering of rewards, indicates that this species is primarily phalaenophilous and secondarily melittophilous, exhibiting a bimodal pollination system.

Predicting physical clogging of porous and permeable pavements

Summary Porous pavements are easily retrofitted, and effective in improving water quality and hydrology, but prone to clogging. Despite being a major determinant in the lifespan of porous pavements, there is limited information on the physical clogging processes through these systems. The aim of this study was to understand the main physical processes that govern physical clogging and develop a simple black-box model that predicts physical clogging. The key variables that were hypothesised to influence clogging were pavement design and climate characteristics. Two compressed time scale laboratory experiments were conducted over 3 years on three common porous pavement types; monolithic porous asphalt, modular Hydrapave and monolithic Permapave. Pavement design was found to be an important role in clogging. Permapave did not clog even after 26 years of operation in simulated sub-tropical Brisbane (Australia) climate while porous asphalt and Hydrapave clogged after just 12 years, from surface clogging and geotextile clogging, respectively. Each system was tested using two different dosing patterns: (1) continual wetting with no dry periods and (2) variable inflow rates with drying periods (i.e. representing more natural conditions). The latter dosing method approximately doubled the lifespan of all systems suggesting the influence of climate conditions on clogging. Clogging was found to be highly correlated with cumulative volume and flow rate. A simple black-box regression model that predicts physical clogging was developed as a function of cumulative volume and Brisbane climatic conditions. However it is very likely that the shape of this regression is general, and that it could be calibrated for different climates in the future.

Surface clogging process modeling of suspended solids during urban stormwater aquifer recharge

Aquifer recharge, which uses urban stormwater, is an effective technique to control the negative effects of groundwater overexploitation, while clogging problems in infiltration systems remain the key restricting factor in broadening its practice. Quantitative understanding of the clogging process is still very poor. A laboratory study was conducted to understand surface physical clogging processes, with the primary aim of developing a model for predicting suspended solid clogging processes before aquifer recharge projects start. The experiments investigated the clogging characteristics of different suspended solid sizes in recharge water by using a series of one-dimensional fine quartz sand columns. The results showed that the smaller the suspended particles in recharge water, the farther the distance of movement and the larger the scope of clogging in porous media. Clogging extents in fine sand were 1 cm, for suspended particle size ranging from 0.075 to 0.0385 mm, and 2 cm, for particles less than 0.0385 mm. In addition, clogging development occurred more rapidly for smaller suspended solid particles. It took 48, 42, and 36 hr respectively, for large-, medium-, and small-sized particles to reach pre-determined clogging standards. An empirical formula and iteration model for the surface clogging evolution process were derived. The verification results obtained from stormwater recharge into fine sand demonstrated that the model could reflect the real laws of the surface clogging process.

Onsite wastewater nitrogen reduction with expanded media and elemental sulfur biofiltration

A passive biofiltration process has been developed to enhance nitrogen removal from onsite sanitation water. The system employs an initial unsaturated vertical flow biofilter with expanded clay media (nitrification), followed in series by a horizontal saturated biofilter for denitrification containing elemental sulfur media as electron donor. A small-scale prototype was operated continuously over eight months on primary wastewater effluent with total nitrogen (TN) of 72.2 mg/L. The average hydraulic loading to the unsaturated biofilter surface was 11.9 cm/day, applied at a 30 min dosing cycle. Average effluent TN was 2.6 mg/L and average TN reduction efficiency was 96.2%. Effluent nitrogen was 1.7 mg/L as organic N, 0.93 mg/L as ammonium (NH(4)-N), and 0.03 as oxidized (NO(3) + NO(2)) N. There was no surface clogging of unsaturated media, nitrate breakthrough, or replenishment of sulfur media over eight months. Visual and microscopic examinations revealed substantially open pores with limited material accumulation on the upper surface of the unsaturated media. Material accumulation was observed at the inlet zone of the denitrification biofilter, and sulfur media exhibited surface cavities consistent with oxidative dissolution. Two-stage biofiltration is a simple and resilient system for achieving high nitrogen reductions in onsite wastewater.

Characterization of Infiltration Capacity of Permeable Pavements with Porous Asphalt Surface Using Cantabrian Fixed Infiltrometer

AbstractPorous asphalt is used in Permeable Pavement Systems, but it is sensitive to surface clogging, which leads to a loss in its infiltration capacity. Test methods based on the use of permeable pavement models, which are manufactured in a laboratory and assessed under different clogging conditions, such as slope, rain, and runoff, have been widely applied to the study of permeable pavements with concrete blocks but not to the study of porous bituminous mixtures. The Cantabrian Fixed (CF) Infiltrometer has been used for the study of porous asphalt with void percentages between 20 and 33%. Three clogging scenarios were studied: 1) newly placed surface, 2) surface with an average maintenance level, and 3) clogged surface. Each clogging scenario was tested with five different slopes: 0, 2, 5, 8, and 10% and three repetitions. The direct rainfall simulation was produced by five lines of bubblers over the 0.25 - m2 piece, and the runoff was simulated by one perforated pipe over a plastic ramp at the beginni...

Effects of earthworms on surface clogging characteristics of intermittent sand filters

Intermittent sand filters (ISFs) are effective and economical in treating wastewater, but they are easy to clog up. To explore a feasible and simple method to alleviate clogging, two pilot-scale ISFs were constructed, one of which contained earthworms and the other did not. During the operation, the effects of earthworms on the hydraulic behaviour of ISFs were investigated. The results showed that both ISFs exhibited good performance in wastewater treatment. However, they showed different hydraulic characteristics although operated at the same organic loading rate (approximately 300 g m(-2) d(-1)). The ISF without earthworms clogged only after 53 d operation, and was partially recovered after 7 d resting, but after that, clogging occurred again, and more rapidly than the initial clogging event (40 d). However, water on the medium surface of the ISF with earthworms was not observed during the whole experiments. In addition, 11-13% of effective porosity and 0.015-0.026 cm s(-1) of infiltration rate were measured in the upper 20 cm of the ISF at the end of the experiments. The facts demonstrated that earthworms played a positive role in alleviating clogging and earthworms fed filter could alleviate surface clogging effectively.

Use of dewatered alum sludge as a substrate in reed bed treatment systems for wastewater treatment

In this paper, two laboratory-scale simulated reed beds were investigated for the purpose of assessing the feasibility and effectiveness of using dewatered alum sludge as a possible substrate for wastewater treatment reed bed systems. One horizontal subsurface flow setup and one vertical flow setup were used. The horizontal flow system was planted with Phragmites australis while the vertical flow system was left unplanted. Thus, the latter was more akin to a sand filter system, but was examined with the potential use as a planted vertical reed bed system. The influent source used was farmyard wastewater. It is expected that the present study will provide the basis for long-term and large-scale trials in realizing the concept of integrating “waste” into treatment processes. Results obtained so far have shown that the dewatered alum sludge holds great promise as a low-cost resource media for use in reed bed treatment systems. Appreciable and stable performance was obtained during the continuous operation at high hydraulic, organic and phosphorus loadings. In particular, both wetlands achieved over 90% phosphorus removal, reflecting the significant advantage of this novel approach over conventional reed bed treatment systems. However, extensive research into possible surface clogging and possible release of some substances from the sludge to the treated effluent is necessary to ensure reliability of the system. This will help to make the alum sludge-based reed bed environmentally and economically justifiable.

Runoff and infiltration characteristics of pavement structures—review of an extensive monitoring program

The stormwater runoff and infiltration performance of permeable pavements has been systematically evaluated within an intensive monitoring program. The primary objective of the investigation was to generate a broad database, which enables the development of an advanced simulation module for urban drainage modelling. Over 160 field and lab scale experiments have been completed and analyzed for surface runoff and infiltration characteristics. The test series include several pavement types under various boundary conditions such as diverse precipitation impacts, varying surface slope and layer construction as well as different stages of surface clogging and several base and subgrade layer characteristics. The results represent a reliable and comprehensive database that allows profound conclusions and substantial recommendations.

Nucleoside Phosphorylation by Phosphate Minerals

In the presence of formamide, crystal phosphate minerals may act as phosphate donors to nucleosides, yielding both 5'- and, to a lesser extent, 3'-phosphorylated forms. With the mineral Libethenite the formation of 5'-AMP can be as high as 6% of the adenosine input and last for at least 10(3) h. At high concentrations, soluble non-mineral phosphate donors (KH(2)PO(4) or 5'-CMP) afford 2'- and 2':3'-cyclic AMP in addition to 5'-and 3'-AMP. The phosphate minerals analyzed were Herderite Ca[BePO(4)F], Hureaulite Mn(2+)(5)(PO(3)(OH)(2)(PO(4))(2)(H(2)O)(4), Libethenite Cu(2+)(2)(PO(4))(OH), Pyromorphite Pb(5)(PO(4))(3)Cl, Turquoise Cu(2+)Al(6)(PO(4))(4)(OH)(8)(H(2)O)(4), Fluorapatite Ca(5)(PO(4))(3)F, Hydroxylapatite Ca(5)(PO(4))(3)OH, Vivianite Fe(2+)(3)(PO(4))(2)(H(2)O)(8), Cornetite Cu(2+)(3)(PO(4))(OH)(3), Pseudomalachite Cu(2+)(5)(PO(4))(2)(OH)(4), Reichenbachite Cu(2+)(5)(PO(4))(2)(OH)(4), and Ludjibaite Cu(2+)(5)(PO(4))(2)(OH)(4)). Based on their behavior in the formamide-driven nucleoside phosphorylation reaction, these minerals can be characterized as: 1) inactive, 2) low level phosphorylating agents, or 3) active phosphorylating agents. Instances were detected (Libethenite and Hydroxylapatite) in which phosphorylation occurs on the mineral surface, followed by release of the phosphorylated compounds. Libethenite and Cornetite markedly protect the beta-glycosidic bond. Thus, activated nucleic monomers can form in a liquid non-aqueous environment in conditions compatible with the thermodynamics of polymerization, providing a solution to the standard-state Gibbs free energy change (DeltaG degrees ') problem, the major obstacle for polymerizations in the liquid phase in plausible prebiotic scenarios.

Influence of surface layer on hydrology and biology of gravel bed vertical flow constructed wetlands

In France, gravel vertical flow constructed wetlands (gVFCWs) were adapted to treat raw wastewater, which led to important accumulations of matter in filters (organic and mineral). To prevent clogging, large gravel sizes were employed (O 2-6 mm). The aim of this paper was to present the influences of matter accumulation on the hydraulic and biological behaviour of the system. A one-year survey of accumulated matter content and potential respiration activities was completed in three gVFCWs (operating for 3, 4 and 8 years). Cores were sampled into filters. Results showed a vertical stratification of accumulated matter and respiration rates. Dry accumulated matter quantities ranged from 20 kg m(-2) (3 and 4 years operating) to 80 kg m(-2) in the oldest plant (8 years). Potential respiration was larger in the oldest plant (75g O2m(-2)h(-1)) than in the most recent one (15g O2m(-2)h(-1)). Accumulated matter seemed to play a role both on the water retention (enhancing initial percolation time by 5 times) and biological profile (enhancing microfauna's diversity). Contrary to what is generally proposed in the literature, accumulated matter in French gVFCWs seemed to provide better treatment efficiency without leading to surface clogging compared to systems using sand.

Surface Clogging in an Intermittent Stratified Sand Filter

Accumulation of biomass and deposition of suspended solids at the surface of a sand filter can lead to clogging of the filter media. A laboratory intermittent sand filter column, which included three sand strata, was operated for a period of 806 d before failure occurred through surface clogging. Upon dismantling the column, the cause and effects of the surface clogging were investigated. The main mechanism responsible for sand clogging appeared to be biomass buildup. Maximum loss on ignition of filter media samples was 2.35%, and it occurred in the upper 0.01 m of the sand. There was a reduction in field‐saturated hydraulic conductivity in the top 0.01 m of the upper sand stratum from a value of 1.9 × 10−3 ± 1.7 × 10−4 m s−1 (for virgin sand with an effective size, d10, of 0.45 mm) to 3.5 × 10−5 ± 7.5 × 10−6 m s−1 The soil‐water characteristic curve, which relates the volumetric water content (θv) to the soil suction, also reflected the changes in the filter media due to clogging. The water‐holding capacity greatly increased as biomass accumulated in the filter media. Scanning electron microscopy (SEM) confirmed the existence of a clogging organic layer on the surface of the top sand layer.

Infiltration Considerations for Ground-Water Recharge with Waste Effluent

Water reuse and ground-water recharge can be used to meet the growing demands for water, particularly in arid regions. Ground-water recharge using fresh water or treated wastewater is most often accomplished by infiltration from surface basins. The water percolates through the unsaturated soil region to an underlying aquifer for storage and future use. In the case of wastewater, additional treatment occurs as the effluent flows through the soil. The system hydraulics of recharge basins have been examined through a combination of field and laboratory investigations. These studies indicate that infiltration rates and soil aquifer treatment of wastewater are influenced by soil type and soil profile characteristics, surface clogging material, pond depth, and wetting/drying cycle times. The surface-clogging layer was found to be susceptible to consolidation and to associated reduction in hydraulic conductivity under seepage forces.

Development of a new generation of reed-bed filters in France: first results

Since 1992, Reed-Bed Filters (RBF) wastewater treatment plants have been built to meet the needs of 15 rural authorities and, on an experimental basis, 2 farms to treat milking parlour washwater using this method. This paper presents results obtained at a plant designed for 200 p.e. after 15 months of operation, organic and hydraulic loads being 67% and 115% of the nominal loads respectively. With an overall area of the order of 2.2 m2 per person equivalent, the plant produces an effluent which easily complies with the following water quality criteria : 90 mg l−1 COD, 30 mg l−1 TSS and almost 10 mg l−1 TKN. Phosphorus removal is normally very low. A farm-located experimental plant, receiving milking parlour washwater (COD between 700 and 1400 mg l−1), is providing promising results which will certainly be improved by extending the current RBF areas. RBFs are capable of directly treating raw sewage by applying procedures involving batch feeding and alternating several units operating in parallel; in this way aerobic conditions are maintained and physical surface clogging is controlled with the aid of rooted macrophytes. RBFs used for complementary treatment seem to accept continuously high hydraulic loads.

Development of a new generation of reed-bed filters in France: First results

Since 1992, Reed-Bed Filters (RBF) wastewater treatment plants have been built to meet the needs of 15 rural authorities and, on an experimental basis, 2 farms to treat milking parlour washwater using this method. This paper presents results obtained at a plant designed for 200 p.e. after 15 months of operation, organic and hydraulic loads being 67% and 115% of the nominal loads respectively. With an overall area of the order of 2.2 m2 per person equivalent, the plant produces an effluent which easily complies with the following water quality criteria: 90 mg 1−1 COD, 30 mg 1−1 TSS and almost 10 mg −1 TKN. Phosphorus removal is normally very low. A farm-located experimental plant, receiving milking parlour washwater (COD between 700 and 1400 mg 1−1), is providing promising results which will cenainly be improved by extending the current RBF areas. RBFs are capable of directly treating raw sewage by applying procedures involving batch feeding and alternating several units operating in parallel; in this way aerobic conditions are maintained and physical surface clogging is controlled with the aid of rooted macrophytes. RBFs used for complementary treatment seem to accept continuously high hydraulic loads.

Development of methodology for the optimal operation of soil aquifer treatment systems

Soil aquifer treatment (SAT) systems are used for reclamation of sewage effluent by groundwater recharge. Increasing demand on water supplies has stimulated the production or planning of many SAT systems that will use reclaimed wastewater for groundwater recharge. These systems are comprised of a series of infiltration basins. The design and operation of soil aquifer treatment systems presently relies primarily upon judgment and experience. This research effort is developing a methodology for determining the optimal operation of SAT systems that is based upon mathematically describing the problem as a discrete-time optimal control problem. The resulting mathematical problem is a large-scale nonlinear programming problem. Solution of the problem is being accomplished by interfacing a nonlinear programming optimizer, which is solved by a differential dynamic programming algorithm, with a simulator that describes the infiltration process, unsaturated flow, effects of surface clogging and biological clogging, biological removal of nitrogen and organics. Major efforts are devoted to numerical performance of the optimization model solution, and development of the simulator. Initial results of interfacing the optimizer with the simulator without water quality concern show high convergence rate. The operation pattern determined by this method is reasonable. This new methodology will be a tool for engineers to evaluate choices regarding the potential of the design and operation of SAT systems.

Development of methodology for the optimal operation of soil aquifer treatment systems

Soil aquifer treatment (SAT) systems are used for reclamation of sewage effluent by groundwater recharge. Increasing demand on water supplies has stimulated the production or planning of many SAT systems that will use reclaimed wastewater for groundwater recharge. These systems are comprised of a series of filtration basins. The design and operation of soil aquifer treatment systems presently relies primarily upon dgment and experience. This research effort is developing a methodology for determining the optimal peration of SAT systems that is based upon mathematically describing the problem as a discrete-time ptimal control problem. The resulting mathematical problem is a large-scale nonlinear programming problem. Solution of the problem is being accomplished by interfacing a nonlinear programming optimizer, which is solved by a differential dynamic programming algorithm, with a simulator that describes the filtration process, unsaturated flow, effects of surface clogging and biological clogging, biological removal of nitrogen and organics. Major efforts are devoted to numerical performance of the optimization model elution, and development of the simulator. Initial results of interfacing the optimizer with the simulator without water quality concern show high convergence rate. The operation pattern determined by this method reasonable. This new methodology will be a tool for engineers to evaluate choices regarding the potential of the design and operation of SAT systems.

Improvements in Soil Absorption Trench Design

Improperly functioning soil absorption systems are often cited as sources of groundwater contamination. Clogging of the infiltration surfaces and uneven distribution of wastewater along the length of the trench are believed to be a primary reason for poor treatment. A new soil absorption system design, the capillary seepage trench (CST), is similar to conventional systems except that an impermeable liner is placed at the bottom of the trench. The liner prevents direct percolation and causes the wastewater to move upwardly and horizontally by capillary action before percolating downwards. Preliminary experiments comparing the CST to conventional soil absorption system designs were conducted. Removal of organic matter in the CST was found to be significantly better than in the conventional system. Possible reasons for superior treatment of the CST compared with the conventional system include: increased residence time in the aerobic soil zone and a more even distribution of wastewater along the trench.

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 m 3 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.

Optimizing coagulants and flocculant aids for settling

Different considerations are necessary for optimizing primary coagulant dosage when the coagulant is used alone and when it is used in conjunction with flocculant aids for conventional treatment incorporating sedimentation. Optimization based solely on settled water quality is not wholly satisfactory. If the primary coagulant is applied alone, optimization should be based on an economic analysis relating chemical costs and sedimentation basin costs. If the primary coagulant is used with flocculant aids, optimization should be based on minimizing the clogging of downstream filter surfaces.