Abstract:
A treatment system for removal of contaminates includes the introduction of a flocking agent and the settling of resultant aggregations of particulate material, followed by filtration of the remaining water to remove residual flocking agent and particulate matter. Water thus treated is sufficiently clean to discharge into downstream receiving waters, in an effective and efficient manner, and is sufficiently free of flocking agent to avoid being a hazard to aquatic life. The required dose is activated by a rain gauge which meters rainfall over an appropriate time period and evaluated by the microprocessor.

Description:
REFERENCE TO RELATED CASES 
       [0001]    This application claims the benefits of U.S. Provisional application Ser. No. 61/238,675, filed Aug. 31, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    When it rains on a construction site with exposed soil, rain water can cause the soil to erode and be carried into receiving waters, contaminating them with sediment loads and rapidly deteriorating them. 
         [0003]    Heavy contaminates and light oils can be separated from a fluid stream by drawing from the center of a fluid stream. Fine, suspended particles are the most difficult sediment particles to remove, because they require very long settling times and low turbulence in the fluid stream to settle out. It is also most often these fine particles (mainly clay particles) that contribute the most to turbidity (increased opacity) in the water. 
         [0004]    There are a number of methods and technologies used to remove sediments prior to discharge with varying degrees of efficacy. One method of expediting the removal of these fine suspended contaminants is with the introduction of flocculation agent(s) which are used to cause the fine particles to coagulate and settle more quickly. Most of these have an ionic charge which is opposite that of the particles to be settled. As the sediment particles attach to the flocculation agent particles the aggregate particles become larger and larger and settle more quickly. The disadvantage associated with the use of flocculation agents is that in some cases they may involve the addition of something that may be considered a pollutant, and for waters with fish in them, higher concentrations of flocculation agent can cause an occlusion of the fish gills as the gills function with a charge opposite of the flocculation agent causing the agent to accumulate on the gills which could suffocate the fish and kill them. 
         [0005]    While fish are typically not a concern within sediment basins (ponds) at a construction site, where the flocculation agent is introduced and the fine particles are aggregated and settled out of the rain water runoff, fish are a concern in down stream receiving waters. Therefore, it is important to introduce a proper amount of flocculation agent into the rainwater runoff stream, sufficient to remove fine suspended sediment without excess. For example, a minimum of 0.5 ppm of flocculation agent may be sufficient to remove the sediment particles in a particular rainwater runoff, and a dose above 15 ppm may be toxic to some fish species. Therefore it is critical that the proper amount of flocculation agent be introduced into the rainwater runoff to be certain that there is no chance of the floc being overdosed and discharged into the downstream receiving waters. 
         [0006]    One method utilized to avoid the use of excess flocking agents uses a highly controlled, pump and metering system to carefully meter the water and dose the flocculation agent. The water is then retained in a settling tank for a sufficient period of time to allow the settling of the fine sediments to settle. The water is tested for the presence of residual flocking agent and then discharged into the receiving body of water only if the residual presence of flocking agents is below a minimal value. This, although safe and effective, is very expensive. 
         [0007]    Flocking agents can also be administered by placing the flocking agent into a cloth or semi-porous material sock. This sock is then placed into a gravity flow pipe or pump discharge pipe and, as the water flows through the sock, the flocking agent is slowly released. This is a very crude and risky means of inducing the flocking into the water stream, because dosing rates are virtually impossible to control with any level of precision and an overdose could easily occur. 
       SUMMARY OF THE INVENTION 
       [0008]    This invention treats runoff water which is laden with fine particulate sediment prior to discharge into downstream waters. The invention incorporates a treatment train with a dosing system for introducing a flocking agent and a settling means to allow settling of resultant aggregations of particulate material, followed by filtration of the remaining water through a filter to remove any residual flocking agent as well as particulate matter. Water thus treated is sufficiently clean to discharge into downstream receiving waters, in an effective and efficient manner, and is sufficiently free of flocking agent to avoid being a hazard to aquatic life. 
         [0009]    A series of components are utilized in a treatment train that will clean runoff water. First the required dose is activated by a rain gauge located on a dosing station near the inlet of the sedimentation pond. As the rain occurs, the rain gauge meters the amount of rainfall and sends that data to a microprocessor. The microprocessor will get a signal for each interval of rain (typically 0.01″). The microprocessor can then determine the dose by taking into consideration any number of parameters: antecedent dry period from last rain event, minimum rainfall before dosing will occur, site conditions that will contribute to the runoff, intensity of the rainfall (interval between signals of at least 0.01″), drainage area to the system, time of year, temperature, time to concentration of the runoff, soil types, effluent targets, and target dose concentration. This data will then be evaluated by the microprocessor to determine the precise amount of floc agent to be dispersed. The dosing station is preferably one that uses a finely ground powdered floc agent such as chitosan, metered using an auger with controlled rotation, however any number of feed metering methods may be employed including for example feeding a liquid floc agent by metering with a peristaltic pump. The preferred method of dosing the floc agent is at or near the inlet of the sediment basin so the floc mixes with the turbid influent. As the turbid runoff water enters the pond, mixed with the floc agent, flocculation and subsequent settlement will occur. 
         [0010]    When the pond reaches a certain level, water is skimmed from the storage chamber and diverted by gravity or pump to a filtration vault. The filtration vault will have filters preferably of a polypropylene felt that will remove any unsettled and/or floc&#39;d particles as well as residual floc. 
         [0011]    This system controls the dose of floc agent to a level that the risk of overdosing is minimized, and by the filtration method incorporated any residual floc is removed prior to discharge. The present invention achieves an efficient means for cleaning very fine (typically clay) particles from runoff water, typically the reduction of the clay content of the water to a negligible level. The present invention is capable of removal of 99% of the clay particles in a stream of water with less than 10 minutes of residence time in the filter vault. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a diagram of the overall system for capture and treatment of runoff from a job site. 
           [0013]      FIG. 2  is a detail diagram of the rain gauge controlled floc agent dosing station. 
           [0014]      FIG. 3  Shows the system with the filtration vault located within the sedimentation basin 
           [0015]      FIG. 4  shows the system with the filtration vault located Outside of the sedimentation basin (opposite a weir wall). 
           [0016]      FIG. 5  shows the system utilizing a lift pump to pump the water to the filtration vault located outside of the sedimentation basin. 
           [0017]      FIG. 6  shows the siphon feature associated with the skimmer and filter vault. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]    An exemplary embodiment of the present invention is illustrated as implemented on a construction job site, which can typically introduce a large quantity of fine particulate sediment into the rainwater runoff water. Although the present invention is illustrated in connection with a construction site, the invention is applicable in any situation where fine particulate material is introduced into a water flow and requires removal, whether or not the introduction of the material is the result of soil erosion. 
         [0019]    Prior to start of construction the job site  FIG. 1  topography is analyzed to determine the water runoff flow for the limits of the construction site  8 . The analysis will determine how rain water and/or ground water drains from the site. Typically a site is divided into drainage areas, such as drainage areas  1 ,  2  and  3  illustrated in  FIG. 1 , which are separated by drainage divides  6 . An analysis is also made to determine the surface area in a particular drainage area to determine the volume of rain that will fall on that area for each increment of rainfall. As an example, a sedimentation basin  30  will be constructed at the low point of the drainage area  3 . The drainage divides  6  and diversion berms  4  will divert all runoff water to an influent location  7  of sedimentation basin  30 . At preferably the most concentrated inlet location  7  to the sedimentation basin  30 , is a floc dosing station  33 . Inside of the sedimentation basin  30  is a floating skimmer  31 , a filter vault  32 , and an effluent pipe  34 . Ideally the sedimentation basin may contain a high flow bypass means (not shown) to safely convey extreme storms beyond the flow capacity of the filter vault. 
         [0020]      FIG. 2  shows the core components of the dosing station  33 . This is typically a self contained modular unit which is capable of operating remotely with a battery and solar operated battery charger. The dosing station  33  has a rain metering means (rain gauge)  20 . Each increment of rain (typically at least 0.01″) sends a signal to a microprocessor  21 , which collects this data. The microprocessor will have any number of variables programmed into it which, combined with each increment of rain data, will be used to determine the appropriate volume of floc agent to disperse. The microprocessor will then use programmed variables such as expected runoff for the geographic conditions, rainfall intensity (interval between increments), drainage area, dry period from last storm event, target effluent concentrations, time of year, temperature, and other variables determined to target the best dosage. 
         [0021]    The quantity of flocking agent dosed into the water can be dependant on the quantity of rain as a one dimensional variable or can also include the rate of rainfall over time as a second dimension variable to adjust the dosage of flocking agent. For example the same total quantity of rain falling over a shorter period of time may require a greater quantity of flocking agent than the same total quantity of rain falling over a longer period of time. Also, the same periodic quantity of rainfall with greater or less separation between periods of rainfall may require differentiated treatment dosages. With the incremental rainfall data, the microprocessor then determines the timing and volume of floc agent to disperse. This can be done using either a standard dose of for example 1 gram and sending a signal to dose 1 gram at a time or it can be done by determining the exact amount and controlling the rotation of the auger to meter that precise amount. There are many means of taking this computed data and metering the appropriate dose, including for example using a liquid floc agent and a peristaltic pump to meter the volume. In the preferred example provided, the rain gauge  20  located on the dosing station  33  trips a tipping bucket  26  for each increment of rain. This sends a signal to the microprocessor  21  which uses that signal to process, in conjunction with the other variables, and determines the appropriate dose of floc agent  29  to disperse into the influent water  25 . The microprocessor  21  having computed the volume of floc agent  27  and time to disperse, converts this volume to degrees of rotation of the dosing auger  23  and sends a signal to the motor  24  to rotate the dosing auger  23  by that amount thereby sending the precise dose of floc  29  into the influent stream  25 . 
         [0022]    Locating the dosing station at the most turbid input location is ideal in that it will enable the greatest mixing of the floc agent and the influent stream. The flocked water then enters the sedimentation basin  30  and begins to settle the fine solids and flocked clay particles. As the water level rises in the sedimentation basin  30 , it will raise to the point that the skimmer  31  will begin to flow water into the filter vault  32 . The water that flows into the filter vault  32  has been skimmed from just below the surface so that it has had the maximum settling time and is the cleanest. This water will still contain some solids and floc. The water enters the filter vault  32  and flows through the filters  38  which remove the remaining turbidity causing contaminants, any remaining flocked solids, as well as the residual floc agent. From there the water is released through the effluent pipe  34  to the downstream receiving waters. 
         [0023]    The filters  38  are preferably polypropylene felt and of a spiral wrapped design, to optimize surface area. However the filters can be of many different combinations including sand, fabrics or other media. 
         [0024]      FIGS. 3 ,  4 , and  5  illustrate alternative locations of the filtration vault  32  relative to the sedimentation basin  30 .  FIG. 3  shows the filtration vault  32  inside of sedimentation basin  30 .  FIG. 4  shows the filtration vault  32  is located outside of the sedimentation basin  30 , just opposite of a weir wall  35 . The weir wall  35  could also be simply an embankment. 
         [0025]      FIG. 5  illustrates the filtration vault  32  located outside of the sedimentation basin  30 , at a height which prevents the water from flowing into the filtration vault  32  by gravity. When the filtration vault  32  is located above the level of the water in the sedimentation basin, water can be pumped directly from the skimmer pipe  39  or alternatively, a sump basin  37  can be located within the sedimentation basin  30  and the skimmer pipe  39  can discharge into the sump basin  30 . As the water enters the sump pump basin  37  it is pumped by a lift pump  36  to the filtration vault  32 . 
         [0026]    The present invention enables a calculated and precise dose of floc agent, followed by sedimentation, and then a final filtration step which removes remaining sediments, remaining partially flocked clays, as well as residual floc agent. Thereby insuring that only clean water free of any floc agent is discharged into receiving waters. 
         [0027]    A system designed to implement the present invention can be altered or optimized to address the particular needs, requirements and/or design choices and considerations of the particular installation. For example, increasing the settling time will reduce the load on the filter and increase its life expectancy. Decreasing the settling time will allow a smaller pond to process a greater quantity of rainwater in a given amount of time but will decrease the useful life of the filters because they will be able to process a smaller quantity of water before replacement. 
         [0028]    In another exemplary embodiment, a second skimmer  31  is added to the filtration vault  32  which operates only when the sedimentation basin  30  reaches a certain increased level. This will decrease the load on the filters during most storms yet be able to still treat the higher volume/intensity storms, thereby optimizing the filter life between change outs. 
         [0029]    In further exemplary embodiment, a float controlled metering valve can be installed on the filter effluent pipe  34 , inside the filtration vault  32 , which is float activated thereby increasing the flow of the filters at higher levels of water in the filtration vault. 
         [0030]    In an additional exemplary embodiment,  FIG. 6 , shows the floating skimmer  31  adapted with a one way air release valve  41 . As the water level rises in the sedimentation basin  30 , it will displace the air under the hood of the skimmer  31  through the air release valve  41 . The water will flow through the skimmer pipe  39  into the filtration vault  32 . There is a turned down elbow  42  located on the skimmer pipe  39  inside of the filtration vault  32 . Once the water has achieved an elevation above the top of the skimmer pipe  39  where it enters the filtration vault  32  there will be a sealed (air free) water chamber. Then as the storm event subsides, a siphon occurs until the water level in the filtration vault is below the bottom of the elbow  42  and at that point air will enter and break the siphon. This achieves an increased settling time and capacity between storm events, further reducing load on the filters and further increasing their life cycle. 
         [0000]    Treatment train above