Patent Publication Number: US-2010129895-A1

Title: Biofiltration system for odor control

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to an apparatus and process for treating air streams to remove pollutants. More particularly it relates to a system that allows for remediation of multiple contaminants by contaminant-specific remediation organisms having differing pH and moisture needs, the continuous flow process being performed within an internally segmented unitary housing in which there is no fluid connection between the sectional treatment chambers. 
     2. Description of the Relevant Prior Art 
     Vaporous pollutants, which are frequently toxic or corrosive or both, are created in a multiplicity of municipal, commercial and agricultural processes and become part of output airstreams. Treatment of these output airstreams to strip out the pollutants is important to human health, to prevent damage to equipment, to protect the environment and to provide odor control. 
     The earliest methods used to deal with these pollutants were by physical and chemical processes. The physical processes unfortunately created large amounts of contaminated waste materials that then had to be dealt with. The chemical treatment methods that replaced physical decontamination are well established and reliable, however, they involve the use of hazardous chemicals and are associated with the need for increased safety features that increase the footprint and the operating costs of the units. 
     These drawbacks led to the development of biological treatment of air streams that has proven itself to be effective, safe and cost effective. Such biological treatment systems are capable of treating high flows of contaminated gas having high inlet concentrations of pollutants. 
     A typical biological treatment system involves passing the contaminated air stream through an inert, porous media base that has been inoculated with and supports the growth of specific microorganisms. The contaminated air passes over the organisms which feed on and convert the pollutants into innocuous compounds, thus removing the odor and other undesirable components and allowing the release of remediated air. 
     The whole process taking place within a containment structure which serves as a unit. In instances where the air stream contains corrosive gases, the materials used to form the treatment unit are chosen to be as non-reactive as practical. Issues include treatment unit size, the need to deal with multiple contaminants that require different pH and moisture conditions for the support of the bio-organisms that remediate each of the contaminants and providing a control system that provides maximal remediation with minimal complexity. 
     Some of the most common air stream contaminants include hydrogen sulfide, mercaptans, amines and various organic acids. Hydrogen sulfide gas is toxic and very corrosive and is found in places as diverse as municipal sewage and sewer lines, oil well drilling locations, wood processing plants, and various other municipal and industrial processes in which elemental sulfur comes into contact with organic materials. This is the gas associated with the smell of ‘rotten eggs’. It is very toxic and can kill by asphyxiation, or by explosion. 
     A very effective method for treating hydrogen sulfide is to pass the air containing hydrogen sulfide through a highly porous, chemically inert media that is being bathed in water at a pH in the range of 1.8-2.2. Under these conditions a biological culture can be made to grow on the media and the cultured organisms will use hydrogen sulfide as a food source, converting the hydrogen sulfide to sulfuric acid using oxygen present in the air. 
     Organic Compounds other than hydrogen sulfide can be treated by moving the air containing these organic compounds through a highly porous, chemically inert media at a neutral or mildly alkaline pH while ensuring that the air is humidified and the media is kept moist through supplemental irrigation. Under these conditions a biological culture that will use these organic compounds as a food source can be made to grow on the media and convert those compounds to carbon dioxide and other by-products using oxygen present in the air. 
     Systems that try to simultaneously treat gas streams containing hydrogen sulfide as well as other organic compounds run into the following problem: oxidation of the hydrogen sulfide component of these complex air streams yields a by-product of sulfuric acid that interferes with the development of the biological substrate necessary for the treatment of the non hydrogen sulfide components of the air stream. 
     Oxidation of hydrogen sulfide takes place primarily at low pH conditions, and requires the use of autotrophic Thiobacillus bacteria. The bulk of the other contaminants commonly encountered in mixed contaminant airstreams require the use of heterotrophic bacteria at close to neutral pH conditions. The presence of both autotrophic and heterotrophic bacteria within a single treatment chamber causes a competition between the various bacteria at the required operating conditions. This in turn leads to reduced efficiency in the system because the non-separated fluid sections do not lend themselves to optimizing the pH in the sections of the treatment unit that are dealing with compounds requiring acid vs. neutral or base tolerant strains of microbial flora. It also leads to the need for using an increasingly complex system of trying to balance the pH of the water to the needs of the differing bacterial colonies within the treatment unit. 
     Bonnin et al., in U.S. Pat. No. 5,858,768, describe a system for the biodegradation of sulfurous compounds in combination with the physical/chemical elimination of organic nitrogenous compounds. The system is not continuous for the removal of both sets of pollutants, and though alteration of pH is provided for, the pH parameters described do not provide optimal target pH levels for either the acid or the base environment dependent microorganisms, thus likely leading to less efficiency in clearing Hydrogen sulfide gas. Like Horn, U.S. Pat. No. 5,869,323, Koers in U.S. Pat. No. 5,445,660 describes a system in which the polluted air is passed through at least two or more separate housings for purposes of treating pollutants requiring environments of differing pH and moisture for the biologically active components in the chambers. Needing multiple housings increases the cost and the number of connecting elements, pumps, seals and monitoring devices needed and thus would seem to create a less cost effective approach. Parker, et al in U.S. Pat. No. 7,276,366 describe a vertical treatment unit having two media containment sections within a unitary housing. However, the vertically stacked media sections are separated only by the perforated floor of the upper section. Contaminated air enters through an inlet at the bottom of the unit and passes sequentially upwards through both media bed sections and thence out an exhaust stack. Water for moistening the media bed, carrying in microorganisms or altering the pH can be introduced atop either the top section or the lower section in a reverse flow direction to the movement of air in the unit. However, any fluid entering the top section must percolate into and through the lower bed in order to enter the sump and exit the system, this raises the pH in the lower section. A complex, computer controlled system is required to periodically, and for a predetermined run time, alternate between passing fresh irrigating water, or recycling acidifying water from the sump into one or the other or both bed sections in an attempt to maintain pH in the 1.8-2.2 range for optimal clearance of Hydrogen sulfide in the lower (“Bioscrubber”) section. The upper (“Biofilter”) section pH being controlled in a similar manner such that it suits more alkaline loving microorganisms. Having a fluid connection between the bioscrubber and biofilter sections of the treatment unit leads to increased complexity of the control system and decreased specificity of the pH levels for optimal colonization of the microorganisms in the two sections of the treatment unit. As with any such media bed system, the vertical height is limited by the need to prevent compaction of and channel formation within the media beds. A series of these vertical units would be needed to handle larger volumes of contaminated air, resulting in the need for additional computer control systems which of course leads to a higher cost for the system. 
     Past designs for systems capable of remediating air streams containing mixed pollutants have suffered from the need to use multiple units for large scale operations and that led to increased installation costs. The fluid connection between the sections of the treatment units created alterations of pH that reduced the units&#39; decontamination cost-efficiency. Some have required complex control systems to try and maintain proper pH, moisture levels and microbial populations tolerant of the pHs of the varying pollutants in the air stream because of the fluid communication between the internal sections of the unit. 
     Statement of the Objectives 
     Accordingly, it is an objective of this invention to provide a unitary housing treatment Unit having no fluid connection between its two or more, separated, fluid containing, internal treatment chambers. 
     A further objective is to provide a unitary, corrosion resistant, housing that can be created having the structural strength allowing for its use in large commercial and municipal reactors, yet also having a flexibility of design allowing for use in small sized reactors. 
     Another objective is to provide a treatment unit that allows optimal control of pH, moisture levels and microbial population purity within the separated internal sections of the structure that are intended to separately and sequentially remediate Hydrogen sulfide, which requires microorganisms that are very acid tolerant, and other pollutants such as mercaptans, amines and various organic acids that are dealt with by microorganisms that can only flourish at neutral or basic pH levels. 
     Another objective is to provide a system that is easily managed and largely self-regulating thus reducing operating costs. 
     SUMMARY OF THE INVENTION 
     The invention involves the creation of a unitarily housed air treatment system for the remediation of mixed air stream pollutants that embodies at least two separate treatment chamber sections, at least one of which requires the presence of microorganisms tolerant of a highly acidic pH while another or other sections require a neutral or basic pH. The design allows complete independent control of media bed pH, moisture levels, and microorganism population types within the two treatment chamber sections. The air pathway is from below upwards with countercurrent moisture application from above down in both treatment chambers. The only connection between the first and the following section(s) is an air-communication only channel which allows air that has passed through the more acidic treatment chamber wherein Hydrogen sulfide and like products are reduced, to move into the Unit&#39;s further chamber(s) without altering the moisture and pH thereof. Sensors and regulators are used to keep pH, moisture levels and rate of flow within predetermined parameters in both treatment chambers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 . Presents a longitudinal cross sectional view of a treatment unit. The drawing is not to scale, the vertical component having been expanded for clarity. 
         FIG. 2  Presents a transverse sectional view of the same unit looking down from above, but with the roof section removed. The drawing is not to scale, especially as regards the width which is exaggerated in respect to the length of the unit 
         FIG. 3 . Presents a detail of the air-communication only channel that separates the first treatment-chamber (“bioscrubber”) and second treatment-chamber (“biofilter”) sections of the treatment unit. 
         FIG. 4  Presents a diagrammatic representation of the control system, electrical and water supplies and the waste water removal system of the treatment unit. 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     Further objectives advantages and novel features of the invention will be apparent to those skilled in the art from the following detailed description when taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention. 
     As seen in  FIG. 1 , the invention involves the creation of a unitarily housed gas stream purification treatment unit (“Unit”)  1  fabricated from fiber glass reinforced plastic (FRP), or other chemical resistant material such as fiberglass, plastic, stainless steel; the Unit  1  being internally divided into at least two treatment chambers having no fluid connection, a bioscrubber (“Scrubber”) section  100  and a biofilter (“Filter”) section  200  that are connected by a gas communication only channel (Gas Channel)  40 ; 
     Gas Channel  40  creates a non-fluid connection between Scrubber and Filter sections  100  and  200 ; the totality of the treatment Unit  1  externally comprising a front wall  110 , a Scrubber section  100  roof  109 ; a dome shaped Filter section  200  roof  201 , a rear wall  202  and a floor  203 ; the whole being fabricated of FRP, or of FRP reinforced by steel support members (none depicted) that are sealed away from the internal chambers of said Unit by being coated with a chemical resistant material when issues of size and weight dictate such reinforcement. Note: a pair of side walls  42   FIG. 2 and 43   FIG. 2  are not indicated as such in this view. 
     Continuing with the view shown in  FIG. 1 , a contaminated gas stream enters the Scrubber section  100  via the driving force of a fan (not shown), the gas stream flows in the direction indicated by the arrow  41  and thus into an inlet flange assembly  101  that is affixed to the Scrubber section  100  front wall  110 ; the gas then moves into a gas stream entry plenum  102 ; a perforated plate  112  delineates the top boundary of the plenum  102  and also serves as the bottom limit of a media section  103 ; the lower limit of the gas stream entry plenum  102  is formed by a perforated plate  113  which also serves as the top boundary of a sump  114  of Scrubber section  100 ; the gas stream next moves up into media bed section  103  after which it passes into a moisturization chamber section  107  where it passes beneath a series of sprinklers  105  located on a set of water lines  106  that are attached to a series of FRP cross braces  108  which in turn are affixed to the undersurface of the roof  109  of Scrubber section  100 ; 
     The gas stream, now cleansed of some contaminants moves up and over the Scrubber section  100  rear wall  111 , which will be noted extends below to the floor  203  and ends above at a short distance beneath the Scrubber section  100  roof  109 , forming the front wall of the Gas Channel  40 ; a front wall  204  of the Filter section  200  forms the rear wall of Gas Channel  40 ; the Filter section  200  front wall  204  depends down from the Filter section  200  domed roof  201  and ends below at a perforated floor plate  205 . 
     Perforated floor plate  205  serves as both the base of the Filter section  200  media bed  206  and as the top plate of the Filter section  200  sump section  217 ; the Filter section  200  sump  217  is drained by overflow drain  216  that allows water collected therein to be evacuated such that the sump  217  contains a headspace which serves as an entry plenum into which the gas stream being treated passes from Gas Passage  40 . 
     Following which the gas stream moves up through perforated floor plate  205  into the Filter section  200  media bed section  206 , then up into a moisturization chamber section  207  where supply water is added by a series of sprinklers  208  attached to a water inlet line array  209   FIG. 1  (best seen in  FIG. 2 ) that is supported along a pair of longitudinal FRP supports  210  which in turn are affixed to a series of FRP cross supports  211  that are attached to the Filter section  200  perforated, internal top plate  212 . 
     The Filter section  200  perforated internal top plate  212  also serves as the floor of a gas stream exit plenum  213  where the purified gas collects and then moves up into a set of exhaust stacks  214  and finally into the ambient air mass. 
     Scrubber section  100  media bed section  103  contains an inert media  104  (cross hatching), such as conventional foam, reticulated foam, plastic or other such acid resistant synthetic materials; whichever media material is selected for use, that material is inoculated with and serves as the support substrate for colonies of autotrophic micro-organisms that feed on Hydrogen sulfide gas, the primary component of the gas stream removed in Scrubber section  100 ; less quantitavely prominent organic sulfides, ammonia, amines and such compounds are also removed in the scrubber  100  media bed  103 . 
     Filter section  200  media bed section  206  contains an inert medium  215  (cross hatched area) such as granulated carbon, other carbon based media, wood chips, engineered media, lava rock or other such media that are inert to mildly alkaline solutions; whatever the media type selected for use, the media material is inoculated with and serves as the support for heterotrophic microorganisms that thrive in a neutral to mildly alkaline environment. These heterotrophic organisms digest organic nitrogenous compounds and other residual contaminants, thus removing them from the gas stream. 
     Note, the use of the terms “Scrubber” and “Filter” in the preceding and following text refers to two sections of the treatment Unit  1  that are designed to operate on differing component compounds of a multiply contaminated gas stream. Both use microorganisms colonized on base media for purposes of gas stream remediation. Neither section relies on a physical “filtration” system of purification. In all instances, the term “Scrubber” refers to the first air treatment chamber, which is kept at a low pH range, optimally pH 1.8 to 2.2, whereas the term “Filter” refers to the second air treatment chamber which is kept at a neutral to mildly alkaline pH range. 
     The microorganisms  104  and  215  respectively in the Scrubber and Filter  100  and  200  media bed sections  103  and  206  require a moist environment; moisturization is provided by sprinkler sets  105  and  208 , the flow of water from which creates a counterflow movement of water down though the media beds  103  and  206 ; initially, the water entering both the moisturization chambers  107  and  207  is fresh inlet water from an outside source (not shown); that water having first been conformed to a specific pH range by a control system (not shown) that will be described later and presented diagrammatically in  FIG. 4 . 
     pH regulated water from an external source continues to be the only moisturizing water used in Filter section  200  as long as the treatment Unit  1  is in operation. However, the digestion of hydrogen sulfide gas in the Scrubber section  100  leads to the formation of Sulfuric acid that mixes with and increases the acidity of the water to an undesirable pH as it passes down though the Scrubber section  100  media bed  103 ; this problem is corrected as follows: the hyper acidulated water passes down through air plenum  102  and then through perforated plate  113  into sump  114 ; some of the hyper acidulated water passes out of the system through a scrubber overflow drain  116 ; fresh water from an external source (not shown) is mixed in with the remaining hyper acidulated water in Scrubber section  100  sump  114  in order to bring the water into the proper pH range of 1.8 to 2.2, following which pH modification, the water is re-used in the Scrubber section  100  moisturization chamber  107 . 
     No water is recirculated through the Filter section  200  media bed  206  which requires a neutral to alkaline pH and the water flowing into sump  217  passes through overflow drain  216  and is disposed of via the external drain system (not shown). 
     A Scrubber section  100  drain  117  (best seen in  FIG. 2 ) is controlled by a valve  118   FIG. 2 ; when fully emptying Scrubber  100  is indicated, water exiting this drain passes into a waste water line  119   FIG. 2  and thus out of the system. 
     When viewed from above as in  FIG. 2 , some further aspects of the invention, and other spatial aspects of features seen in  FIG. 1  can be viewed. A brief review of the dynamics of the working of the system follows for the purpose of orienting the process within this view looking down into the Unit  1  with the roof sections  109   FIG. 1 and 201   FIG. 1  removed. 
     Thus, in  FIG. 2  side walls  42  and  43  of the treatment Unit  1  are now seen completing the perimeter shell along with front wall  110  and rear wall  202 ; a recirculation pump  120  is affixed to the Scrubber section  100  recirculation drain  115 ; a recirculation system water line  316  (best seen in  FIG. 4 ) passes out from recirculation pump  120  and forms part of a recirculation and control system that will be described later. 
     A contaminated gas stream enters from a source  41  and after passing from a contaminated gas stream inlet duct (not shown) that is attached to a flange  50 , the gas passes through air inlet  101  and thus through the Scrubber section  100  as described prior. Gas Passage  40  is visible between the Scrubber section  100  rear wall  111  and the Filter section  200  front wall  204 . 
     The topmost layer of the moisturizing support and delivery arrangement comprises: two cross braces  108  in the Scrubber section  100 , and six cross braces  211  in the Filter section  200 . In Filter section  200 , longitudinal support beams  210  are affixed beneath the six cross braces  211  and the water line  209 , comprising a central pipe with eight laterals, each of which terminates in a sprinkler  208  at both ends, is suspended beneath the longitudinal support beams  210  at each lateral offshoot of the sprinkler line  209 . 
     The moisturizing support and delivery arrangement in the scrubber section  100  differs in that no longitudinal support beams are needed because of its short depth. The Scrubber section  100  water pipe  106  with its sprinklers  105  is suspended solely from the paired cross braces  108  to which it is attached. 
     For purposes of further orientation in  FIG. 2 , three circles representing the tops of exhaust stacks  214  that are spaced above the roof (not shown) are seen spaced along the longitudinal center of the Filter section  200 ; the Filter section  200  overflow drain  216  located in the floor  203  is seen centrally at the rear of the filter section  200 . 
     Gas Channel  40 , as shown in greater detail in  FIG. 3  provides a better understanding of the invention&#39;s method of allowing a unitary housing to contain two separate fluid-containing gas stream treatment chambers each of which operates at a separate pH level without fluid connection between the two chambers. 
     Gas Channel  40  is formed anteriorly by the Scrubber  100  back wall  111  that is integrally attached to the floor  203  and ends above at a distance short of the roof  109 ; back wall  111  is integrally attached laterally to the right and left side walls  42  and  43  of Unit  1 . 
     Contaminated gas enters the Scrubber section  100 , and after passing through media section  103  and into moisturization chamber  107  as partially treated gas, the gas stream then follows the pathway shown by the arrow  44  and passes over the Scrubber back wall  111  and then downwards through Gas Channel  40 . 
     The media bed  103  of Scrubber  100  terminates short of the top of the Scrubber section  100  back wall  107 , and in conjunction with the Scrubber  100  overflow drain  116  that prevents excess buildup of exiting water, helps to insure that no water flows from the Scrubber section  100  into the Gas Channel  40  despite the constant counterflow of water entering the Scrubber  100 . 
     Filter section  200  front wall  204  forms the back wall of Gas Channel  40  and is integrally attached above to the Filter section  200  roof  201  and side walls  42  and  43 , ending below a short distance from floor  203 ; thus presenting a space through which the on-moving gas stream, following the direction indicated by arrow  45 , turns into the Filter section  200  combination fluid sump/gas stream entry plenum  217 ; the gas stream then moves upwards through the Filter section  200  media bed  206 , etc. as described prior. 
     As described prior, overflow drain  216  removes excess water from the Filter section  200  sump  217  and sends it into a waste water drain, thus preventing a backup of the treatment water from the Filter section  200  into the Gas Channel  40 . 
     A control panel (“Panel”)  47   FIG. 4  houses the electrical and electronic components that control the electrical power cutoff, gas stream entry fan, moisturizing, recirculation and pH management systems; the Panel presents with a main power switch  300 ; a fan switch  301 ; a recirculation pump indicator light  302 ; a flow relay  303 ; a power switch  304 ; a pH meter  305  and a timer  306 . With the main power switch  300  turned on, the treatment Unit  1  is ready to operate. Note: because the actual flow patterns of the gas and moisture streams as well as most of the structural components of the treatment unit have already been described, only descriptive text related to pH management, moisture levels and such functional considerations follows. 
     Continuing with the view presented in  FIG. 4 , when fan switch  301  is activated electrical current passes on into an electrical power wire  324  to a gas stream inlet fan  307  which then drives the gas stream into the treatment Unit&#39;s  1  gas stream inlet  101 ; note, the fan can alternatively be mounted in the incoming ductwork outside said treatment unit (not shown), or housed within the treatment Unit&#39;s  1  gas stream inlet  101 . 
     Water from an external source (not shown) enters via a water inlet valve  308  and thus into a fresh water line  309  where it passes through a pressure regulator  310  then a pressure gauge  311 ; at this point the water line  309  splits into two separate supplies, one line, a Filter section  200  inlet water line  312 , which always delivers only fresh water, passes through a solenoid valve and its associated electrical control wire  314  that is activated by the timer  306  located in control panel  47 ; timer  306  is set to intermittently spray into the Filter section  200  moisturization chamber  207  using the Filter section  200  sprinkler sets  208  described prior; a port and valve  48  arrangement is located on inlet water line  312  for adding inoculation material, nutrients and other such agents to the Filter section&#39;s  200  media bed  206 . 
     The second branch off from fresh water line  309  is a make up water line  313  which first passes through a rotameter  315 ; the rotameter  315  is adjusted after use and trial to provide a pre-set, stable rate of flow of water to the Scrubber sump  114  from whence the water is then drawn into a recirculation system water line  316  by a recirculation pump  317  which is activated when pump power switch  304  is set in the on position and the signal from pump power switch  304  is carried to the recirculation pump  317  via an electric power line  323 ; after passing through the recirculation pump  317 , the water passes by a pressure gauge  318  then past a pH probe  319  that sends a signal via an electrical control wire  320  to the pH meter  305  in control panel  47 ; continuing past the pH probe  319 , the water passes through a flow transmitter  321  the signal from which passes via an electrical control wire  322  sequentially into indicator light  302 , flow relay  303  and thus to pump power switch  304 . Flow transmitter  321  serves as a fail safe device and should the water level in the system fall below a critical level, the flow transmitter&#39;s  321  altered signal intensity reaches the flow relay  303 , which in turn will trip the pump power switch  304 , thus turning off the recirculation pump  317  and preventing damage to same; having passed by flow transmitter  321 , the water next passes a port and valve  49  located on recirculation line  316 ; port and valve  49  serve to allow addition of inoculant material, nutrients and other such agents to the scrubber&#39;s  100  media bed  103  as needed; finally, the pH corrected water is delivered to the Scrubber section&#39;s  100  internal sprinklers  105 , the placement of which was described prior. 
     Because the Scrubber section  100  uses water from the Scrubber sump  114  mixed with some fresh water to maintain an optimal pH in the Scrubber section  100  media bed  103 , provision is made for some excess water to escape via an overflow drain system comprising an overflow drain  116  and an overflow drain line  325 . Overflow drain line  325  has a trap  326  for the prevention of back flow into the Scrubber section  100  sump  114 . 
     Both Scrubber section  100  and Filter section  200  sumps  114  and  217  have access to a main drain line  327   FIG. 4  that exits into a general drain line (not shown); should need arise to drain the system entirely, opening valve  118  drains the Scrubber sump  114 ; Filter drain  216  is continuously open and has a trap  329  to prevent backflow into the Unit  1 , although an optional valve closure could be used to eliminate the need for provision of a trap on drain line  327 . 
     Note: although they are not part of the control system, exhaust stacks  214  (represented by arrows indicating the final direction of the gas stream flow) are shown for purposes of orientation. 
     A differential pressure gauge array  330 , for the Scrubber section  100 , which serves to register the pressure differential at the inlet and exit peripheries of the media bed  103 , comprises an externally visible differential pressure gauge attached to a pair of pressure sensitive probes  51  and  52 , one of which probes  51  is situated in Scrubber  100  air entry plenum  102  and the other of which probes  52  is situated in the moisturization chamber  107 , thus bracketing the media chamber  103  of the Scrubber  100  and allowing determination of and serving warning of bed-compaction or other such problems if the inlet and exit pressure differential becomes too great. 
     A differential pressure gauge array  331 , for the Filter section  200 , which serves to register the pressure differential at the inlet and exit peripheries of the media bed  206  comprises an externally visible differential pressure gauge having a pair of pressure sensitive probes  53  and  54 , one of which probes  53  is situated in Filter  200  air entry plenum  217  and the other of which probes  54  is situated in moisturization chamber  207 , thus bracketing the media chamber  206  of the Filter  200  and allowing determination of and serving warning of bed-compaction or other such problems if the inlet and exit pressure differential becomes too great.