CA1036952A - Process for the treatment and disposal of septic tank effluents - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A process to remove contaminants from septic tank effluents by the conversion of the septic tank anaerobic treatment process to that of aerobic treatment. The new process multiplies the effluent treatment effectiveness by passing the effluents through an exposed bed of adsorptive and oxidative coal particles. In practice the effluents are intercepted as they are discharged from the tank and the treatment bed they are passed through is not more than 12 inches in depth. This allows for a rapid turnover of oxygen through the bed between periods of effluent loading and unloading of the bed. By maintaining an effluent level below that of the top of the coal particles all decomp-osition odours are removed. Further treatment is provided as the treated effluent is discharged into an effluent dispersal field or into an interim sewage collection line by the use of the coal particles as permeable effluent distribution media. Effluent from this treatment process is reported by Pollution Control Authorities to be better than Level "A" of the "Minimum Requirements for disposal of Municipal and Domestic Wastewaters to surface waters".

Description

~0369SZ
Thi8 invention relates to ~ process for removing cont-aminant6 from se~tic tan~ effluent~ prior to their di~-charge to a ~eptic tank di~posal field or an interim sewage ~ollection ~y~tem.

of major importance to the health and well-being of all mankind is the availability of a safe way to dispose of his own ~astes, preferably in a simple, practical and economical manner.

The problem of providing adequate sewage disposal 10 facilities for private homes, subdivisions and outlying developments on the fringes of developing urban areas i8 one that a great many engineers have faced in recent years.
Depending on local and provincial regulations, the 801-utions have ranged from individual building of septic tank systems to sophisticated packaged treatment plants.
In general however, the individual septic tank and drain field (or pit) ~ystems have prevailed and served until public health considerations brought the installation of public sewers.

Although public health officials and sanitary engineers are not generally in favor of the widespread use of temp-orary septic systems in suburban areas, the urgent need and demand ~or more new and better homes cannot be delayed.
The fact that engineering design data was frequently lacking~ that ~oil and drainage conditions were not always favorable, has not prevented the wholesale u~e of septic sy~tems, but has demonstrated the urgent need to upgrade the treatment effectiveness of the septic sewa~e treatment and disposal system.

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1036g52 In a recent report done for the Regional District of Central Okanagan, B.C. Dated JUly 1974. it i~ stated that " It became increasingly evident during the course of this ~tudy that, until quite recently, little or no consideration ha~ been given to a long term solution to septic tank sludgedisposal. Govcrnment regulatory agencie~ ~eem to have considered th~ septie tank form of se~age treatment as merely an interim situation, in many areas, until full ~cale se~age collection and treatment syste~s wer~ inst-10 alled. Recent experience has shown however, that the useof septic tank~ i~ continually on the increase as lnsta ation of 3ewers lags behind the general populatlon growth rate. Once a concentration of population develop~ on sepkic tanks it becomes increasingly mo~ difficult and expensive to provide sewage collection sy~tems. This situation has prompted several communities in the United StatQs to comp-letely re-think their long range plane for ~e~erage systems and to consider the use of septic tank~, in conjunction with a reliable sludge treatment facility, as a viable -~
20 alternative to a conventional collection and treatment~yst~m. This type of thinking has prompted some recent develop~ent~ in both sludge treatment processes and more efficient septic tank and tile field ~y~tems.

m e projections in this report for future ~eptic tank use indicate that septic tankæ will be with U8 for ~any year~ to come, and the study has therefore concentrated on presenting a reliable long range solution to the sludge disposal problem, rather ~han any kind of an interim or hstop gap~ measure.

In the present state of the art, septic tank effluents are discharged from a septic tank directly into a septic disposal field. The e~fluent at thi~ ~tage i~ only part-ially treated (about 30 to 40%), the treatment conai~ting of the settling out of the heavier solids and the anaer-obic decompo~ition of organic matter. The di~charged e~fluents are hlghly septic and odoriferous, contain ~ome hundreds of billiono of bacteria including pathogenic types and viruses. I have also found that the chemical oxygen demand (COD) and the biochemical oxygen demand (BOD) concentration~ of septic tank effluent are comparable with those of medium to strong municipal sewage- This res-ults from the fact that average water consumption i8 gen~rally le~s in isolated area~ than in an urban municip-ality- Furthermore, a~ a result of the anaerobic decompos-~tion of settled solids in the septic tank, most of the COD and ~OD in the effluent i8 in the soluble or colloidæl form. For the same reason, almost all forms of phosphorus are converted to soluble orthophosphates. These facts are of significance to the present invention because the removal of the aforementioned untreated contaminants now disch-arged in septic tank effluents would result in the prov-ision of tertiary and secondary type treatment at the septic tank treatment stage.

The principle object of this invention i8 to upgrade the degree of sewage treatment effectiveness now obtained in conventional 6eptic tank disposal systems, 80 that the eff-luent after treatment will meet the water quality standards 9Qt by pollution control agencies for the discharge of water to surface waters--4- 103~SZ

Another object of the invention is to maximize the degree of ~sptic tank effluent treatment by intercepting the effluent a~ it i8 discharged from a ~eptic tank and multiplying effluent treatment effectivene~s by converting the anaerobic effluent treatment process to an aerobic effluent treatment proce~s.

Still another object is to provide a septic tank effluent treatment proce~s by means o~ which harmful bacteria and microorganism~ including pathogens and virus ~8 are removed by filtration without the u~e of additional treatment chemicals.

A further object of thi~ invention i8 to provide a process by mean~ of ~hich harmful contaminants are removed from septic tank effluents prior to their di~charge .
A still further object of thi~ invention i8 to provide a ~QptiC tank effluent treatment procQss wherein a certain degree of both tertiary and secondary treatment is given eptic tank effluents as they are discharged from the septic tank by pa~sing the ef~luent through shallow exposed filtration-adsorption-oxidation bed~
containing certain gradation~ of ~elected coal treatment ~edia through which a constant flow of air i8 permitted to circulate between intermittant period6 of effluent loading and unloading of the effluent treatment bed.

An additional object of thi~ invention is to eliminate the need, the labor and expen~e of cleaning the effluent treatment bed. In the pre~ent invention, all waste6 would be re~oved and returned to the septic tank by filter 10.~695Z

backwashing to settle out a~ sludge.

Yet another object of the pre3ent invention i8 to upgrade the wa~er quality of the effluent on its d is-charge,to a level acceptable to pollution control agencies for discharge as treated water into a disper6al field or into an interim 6ewage collection line of an unsewered small community.Wherein,by the u~e of a per-forated sewage collection line,installed for the pur-pose of collecting sewage from homes serviced by septic tanksewage installations, and carrying such ~ewage through areas with a more porous soil structure, whereby the se~age may ~eep and disperse over a greater area.
In the invention, the perforated ~ewagc collection line is laid within a surround of graded selected adsorptive coal through which~all incoming or outgoing effluent seepage would pass and ~ould be treated thereby, to en~ure that the effluents carried in the sewage collection line will be protected from the inflo~ of untr~ated watera and that the waters carried therein may recieve additional treatment on their way to a main sewage collection line, to a holding lagoon or dispersal into surface waters-Other objects and advantages will become apparentfrom the following desciption of the invention and the accompanying drawing wherein there is ~hown schematically a system for performing the method of the invention.

The process of the present invention provides a method of intercepting septic tank effluents as they are di~-. .
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-6- lC1~9SZ

charged from a ~eptic tank and treating them by filt-ration, adsorption and oxidation within a ~ingle treat-ment bed to remove the contaminants, bacteria and micro-organisms~ pathogens and virus'e from the highly septic raw wastewater. Thereafter, discharging the treated effluent into a water disper~al field or into the int-erim se~age collection line of a small community which line comprising a perforated pipeline laid in selected coarsely graded coal materials to provide further treatment to the effluent~ carried therein and to ensure treatment to incoming or outgoing effluents from ~uch ~eepage water In accordance with the invention a filtration, adsor-ption a~ oxidation bed i~ provided, the bed comprising an expo~ed, horizontal container of shallQw depth, cont-aining therein coarsely graded selected adsorptive coal materials for the greater part of it~ length and a small section of finer sand particles. The intercepted effluent discharge from the septic tank is cau~ed to flow through the treatment bed in the direction from the coarse coal particles to the finer sand particles. The shallow depth and coarse gradation of the coal particles in the treat-ment bed en~ures a rapid turnover and con~istant ~upply of oxygen to circulate through the bed during and between the inter~ittant effluent loading of the bed and unload-Ing thereof. All wastes from the bed are removed by backwashing and flushed back to the septic tank to settle out a~ sludge.

Also in accordance with the invention a filtration adsorption and oxidation treatment media is provided :
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~03695Z
to serve a~ a permeable distrib~ltion media surrounding a perforated interim ~ewage collection line lying abov~
a permanent sewer line. The media compri~e~ coarsely graded selected adsorptive coal materials through which all ~eepage~pa~ and are treated thereby. ~hu~ ensuring that the water quality of the septic tank effluents after the foregoing treatment and discharge to the interim sewage collection line i8 maintained.

Referring to ~ig. 1, the filtration, ad~orption and oxidation system of the invention comprises a filter indicated at 20 which i~ divided into three treatment section~, a sediment screen indicated at 25, an ad~orp-tive selected coal section indicated at 21, and a filter ; comprieing f~ner sand particles indicated at 22. The intercepted sQptic tank effluent to be treated i8 passed through the sediment screens 25 to the top of the filter 20 through a conduit 13. The filter 20 i8 impervious on the floor, the two ends and the sides. It has a centre board running from the top of the filter for the greater part of the length indicated at 24. The floor of the filter i8 sloped from the top of the filter 20 to~ard~ the end of the centre board indicated at 24 the 810pe of the floor is then reversed thus allowing the efflue~t to flow by gravity toward~ the end of the seleeted coal filter 20.
The effluent then passes throuqh a 8mall sand filter ind-icated at 22. The effluent from the sand filter 22 may be removed by a conduit 14.

In accordance with the invention the filter 20 i8 comp-rised of two discreet sect~ons of filter media including 1(~3~i952 a longer ~ction 21 of relatively coar~e select~d coal particles, and a ~maller section 22 of fin~r particles.
The actual range of particle ~ize in any one instance may be varied depending on the nature of the effluent contaminantstO be removed. Pre~erably the particles in the longer section 21 are of material of lower den-Bity than that of the particles of the smaller section 22.
The longer section 21 may be, for example, formed of sel-ected, crushed subituminous or lignite eoal whi~e the ~maller section 22 may be composed of fine ~and. The difference in the density help~ to maintain separation be~ween the ~eçtions pQrticularly during backwashing operations.

The present invention has t~o important aspects- The first i9 that the septic tank effluent to be treated is first intercepted as it iB discharged from the septic tank and is pa~sed through a filtration, adsorption and ox-idation filter composed o~ a longer section of coar~e and a ection of finè media. The other aspect i8 that th~ ~ffluent after treatment having attained a high d~gree of water quality i8 further traated to maintain this ef f luent quality , by bedding efflu~nt dispersal lines or the perforated collection line of any interim sewage collection system in the same eelected coarsely graded adsorptive coal treatment media as iB used in the filter-While the desirable size range of the filter mediamay vary depending on the nature of the effluent cont-aminants to be removed and the amount thereof, the part-~ 036sszicles of the COarse section 21 ~hould be substantially larger in diameter than tho~e of the fine ~ection 22. The coarse particles may range, for example from 60 me~h ~creen size to 3/4 inch mesh ~creen size. A highly satisfactory material for use in the section 21 i8 subbituminous or lig-nite CQal. It i8 a highly ~atisfactory filtration, ad~orpt-ion and oxidation media and i8 of relatively low co~t- The coarse section 21 when placed in exposed beds ~hould prefer-ably have a depth of not more than 12 ~nches and the level of effluent in the bed should not be above 8 inches as measured from the kottom to maintain comPlete odour control-The section 22 i9 preferably formed of a relatively densematerial such as silica sand- The particle size should be ~ub~tantially smaller than the Particle size of the coarse section- The æand may range in 8iZ~ from between 0-04 to 0.01 inch. Other satisfactory dense materials will occur to tho~e skilled in the art- The section 22 should have a depth of at least 3 inches and preferably a depth of bet-ween 6 to 12 inches-After a period of about a month the filtration, adsorp-tion and oxidation bed will accumulate certain windblown and degradation wa~tes and should be cleaned- Thi~ is done by a rever~e flow of water through the filter bed~-Clean water from any suitable source is pumped by pump indicated at 16 through conduit 19 and in a rqver~e flow direction through the smaller ~ection 22 and the longer sect~on 21 through conduit 12 and returned to the first chamber of septic tank indicated at 11-In areas where a h~gh water table create~ disposal fieldproblems,the filtration, adsorption and oxidation bed used for the treatment of septic tank effluents may be placed above ground. In this ~ituation, the circulating pump 16 and piping indicated at 26 would be put to use to pump the septic tank effluent from the septic tank 11 into the treatment bed 20.

Refering to Fig 1. The treated effluent di~charged from smaller section of the treatment bed indicated at 22 pa~geg through conduit 14 and then through dispersal conduit indicated at 15 then it is either discharged into a di~persal field ~7 :.i.n case of a single septic tank effluent treatment system or into an interim sewage collection line 18 serving to remove ~eptic tank effluents from installation~ in a smaller community.
Fig 1. Shows adjoining lots in a community served by septic tank treatment 8y~tem8 may share a common lot line 23. This concept saves space and can be made to look attractive as part of a landscaped fenced area.

EXAMPLE 1.
The effectiveness of the filtration, adsorption and oxidation system of the invention for the treatment of ; septic tank effluents is indicated from tests made on an actual operating installation over a period of from April 1974 to December 1974. The installation was made at a home~ite near Metchosen, B.C. The tests were done by the Pollution Control Branch of the Province of British Columbia.

~el Treatment of dome tic sewagle with pu Further to the report dated Jun~e 25th, 1974~ sample~
of influent to and effluent from the treatment system were taken on July 3rd, July 22nd, October 22nd, and December 16th, 1974. The results of the analyses are li~ted in table 1.
The only flow measurement made was on June 17th, at approximately 10 AM, and it indicated a flow rate of 6 gph. If the usual figure of 70 gallons per day per person i8 u~ed for the household, the daily flow would be 420 g~llon~ per day. The volume of the bed empty is 240 cubic feet. The coal used i8 porous to some extent, and the total volume of void~ in the bed i8 probably about 50%. This provides about 120 cubic feet or 750 gallons o~ capacity and at standard flow rate~
~ provides about 1.5 days retention.
; The percentages of reduction in the parameters measured have been classi~ied in Table 2. A high degree of reduct-; ion ha been achieved for ~ome parameters including : æo total and faecal coliform level~ however the effluent i~ definately not suitable for drinking.
The degree of treatment provided by this system i~ better than level "A~ of thenMinimum Req~ements ~or disposal of Municipal and Domestic wastewaters to surface water3".
The amount of sub~urface tile required for this discharge should therefore be reduced.
REDUCTION CLASSES
Class ls 100 - 67%~ Class 2s 66 - 34%~ Class 3s 33 _ o% h~
January 22, 1975 Office of the Regional Manager Poll~tion Control Bran~h, Victoria,B.C.
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-12- 10~9S2 TA~LE 1.
PAR~METER INFLUENT EFFWENT ~ REDUCTION CLASS

July 3, 1974 t effluent from treatm~nt bed a~ter 4 montXs) T. Coli~orm 9.2xlO 9.2x104 99 F. Coliform 4.9x105 7 x103 99 Copper 0.10 ppmO ~ 02 ppm 80 Iron 1.1 "0.20 " 82 Lead 0.039 '~0.005 " 87 Mercury 0.16 ppb0-05 10 Nickel 0.01 ppm0.01 ppm %inc 0~14 ~0~03 ~ 77 T70~ Carbon 130~0 n23~0 ~ 82 ¢al~ium 21~2 n 2~3 n 89 Chloride 32 . 5 n28 ~ 0 ~ 14 3 Ha rdness 54 ~ on 5,53 - 9O
Magnes ium 2 ~ 8 ~0 ~13 n 95 An~nonia 48r7 n24.0 n 50 Nitrate 0~002 n0~07 ~ _ Nitrite 0~007 n0~17 ~ ~
20 Oil and Grease27~0 n 2.0 n 93 BOD 152~0 ~13.0 n 91 COD 393.0 n65.0 n 84 pO4 9.45 "8.96 " 9 3 Tota 1 P04 10 . 7 ~8 . 96 " 16 3 Potass ium 14. 6 n11- 4 " 22 3 Di8s . Solids 302 " 294 ~ 2 3 Su8~ Sol~ds 98 " 12 " 88 SP. Conductance 650 530 18 3 Sulphate 7-5 " 5.0 ppm 30 Turbidity 58 9~ 8 83 For the purpose of this appliCatiOn, the following terms are defined~
The word contaminants i~ meant to include all those extraneous dis~olved, ~u~ended or colloidal substances existing as gaseous, llquid or ~olid, in solution or in any state what~oever9 or any baCtQria or microorganism pathogens or viruses which may exi~t in the effluent discharges from septic tank effluents, before or after their discharge.
An inlet screen to the filter bed is a screen that will prevent sediments from the septic tank passing into the fil~er to plug the filter media. It is a screen thzt is opened to allow wastes to be discharged from the filter bed back to the septic tank when the filter 1~ backwa~hed.
The ad~orptive and oxidative filter media in the filter bed is a material which by flow turbulence :and contact stabilization between periods of loading and unloading of the treatment bed with effluent ;20 causes a rapid inflow of oxygen to permeate the bed, and also serves to concentrate food values therein thereby en~uring the gravitation of oxidative bacteria to the food ~ource. The contaminants removed by the treatment media may be adsorpted, absorbed, or entrap-ped in the filter the end result of such treatment is the very rapid decomposition or removal of the contaminants.
The word di~persal has been uæed sometimes inter-changeably with the word disposal because, it is felt, that the high degree of effluent treatment pos~ible by the use of this new system more correctly des~ribes a dispersal of treated effluents rather than a di~p-osal partially treated wastewater.
The drawing of a filter bed shown in Figure 1. is for the purpose of illustration, it will be realized by tho~e familiar with the art that the configuration and process hydraulics of the filter sy~tem may be altered to suit the terrain, landscaping, po~itioning of the home and other rea~ons. Also in many areas local sanitary regulations require that a minimum of 10 70 or ~ore lineal footage of disposal tile field be installed. It can be seen by the illustration that a treatment bed may have one or more centre board~
or berms for the purpo~e of incr2asing ~he lineal footage of the treatment area. It can be seen therefore that the treatment bed may be shown to conform also to almost any treatment or disposal sanitary regulation.
The words "interim sewage collection line" are used to describe a means by which the septic tank sewage generated in a ~mall csmmunity may be collected, treated 20 and dispersed intransit during its carriage to a final di~charge point. Such a line may be laid above a permanent sewer line connected therato at predeter-mined intervals to takeoff surplus water- The upper lin is a perforated pipeline its purpose is to collect and distribute water therefrom into porous ~oil8 along ita length in the manner of a septic di~posal sy~tem.
80th lines are laid in permeable di~tribution media The lower line i8 salvageable and eventually will serve to carry the sewage to a conventional sewage collection 30 system ~hen such gewer line extentions are made.

~ ~.

Having illu~trated and described a preferred embodimant of the invention, it should be apparent to those ~killed in th~ art that the invention permit~ of modification in arrangement and detail. I claim as my invention all such modifications as come within the tru~ ~pirit and ~cope of the appended claims.

No United States or other foreign applications have been filed.

Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method of removing contaminants from discharging septic tank effluents and maintaining such effluents after treatment and prior to their discharge, at an acceptable standard of tertiary-treatment effluent quality suitable for discharge to surface waters including the steps of:

(a) Providing a horizontal effluent filter bed with predetermined adsorptive and oxidative coal filter-medium sizings therein, having a conventional wint-erizing cover means, a screened effluent inlet and outlet means with a conventional backwashing means, wherein said effluent filter bed 18 divided into a smaller filter section and a larger filter section with a solid divider having inset therethrough a screened effluent inlet-outlet means placed there-between, (b) providing an effluent dispersal field in which conventional baked-clay sewage drainage tile or con-ventional perforated plastic sewage drainage pipe is laid within adsorptive and oxidative coal pervious distribution medium, (c) providing an interim sewage collection and dist-ribution leach line in which conventional perforated plastic sewage drainage pipe is laid within adsorp-tive and oxidative coal pervious distribution medium, (d) providing from crushed and screened adsorptive and oxidative coals a predetermined range of filter-medium, dispersal and distribution medium effluent-treatment sizings in which the maximum coal particle sizing is that passing through a standard 3/4 inch mesh screen size and the smallest coal particle size is that retained on a standard 60 mesh screen size (e) providing the crushed and sized adsorptive and oxidative coals of Step (d) for use in septic tank effluent treatment in which (1) said coal particles in which the maximum size is that passing through a standard 18 mesh screen size and the smallest size is that retained on a standard 60 mesh screen size are placed within the aforesaid smaller section of the filter bed, and (2) said coal particles in which the maximum size is that Passing through a standard 3/4 inch mesh screen size and the smallest size is that retained on a standard 60 mesh screen size are placed within the aforesaid larger section of the filter bed as segregated adsorptive and oxidative coal-particle aggregations, in a predetermined range of specific sizings thereof ranging from coarsely granular to finely granular, and (3) said coal part-icles in which the maximum size is that passing through a standard 3/4 inch mesh size and the smallest size is that retained on a standard 2/4 inch. screen size are used as the pervious adsorptive and oxidative disp-ersal and distribution medium in the said effluent dispersal field when the said conventional sewage tile or conventional perforated plastic sewage pipe as described instep (b)are laid therewithin, and (4) said coal Particles in which the maximum size is that passing through a standard 3/4 inch mesh screen size and the smallest size is that retained on a standard 1/4 inch screen size are used as the pervious adsorp-tive and oxidative disparsal and distribution medium in the said interim sewage collection and distribut-ion leach-line when the said conventional perforated plastic sewage pipe as described in Step (c) is laid therewithin, (f) intercepting and conducting the discharging septic tank effluents by means of effluent conduit piping and discharging the said effluent into the smaller filter section of the effluent filter bed by means of the screened inlet to the filter bed, Passing the said septic tank effluent through the finely granular adsorptive and oxidative filter med-ium and removing the septic tank sewage solids there-from, then Passing the said sewage effluents through the filter-bed divider wall by means of the screened inlet-outlet means inset therein,into the filter-bed larger section then passing the said septic tank eff-luents through the segregated adsorptive and oxidative coal filter-medium aggregations in the direction of from coarsely granular down to finely granular to provide tertiary treatment to the said septic tank effluent and thereafter discharging the treated eff-luents from the filter bed by said screened outlet means.

2. A method as claimed in Claim 1. in which discharging septic tank effluents are intercepted and conducted by conduit means to an effluent filter bed consisting of a smaller filter section and a larger filter section, removing the septic-tank effluent solids therefrom prior to discharging the said effluents into said larger filter section, by passing the said septic tank eff-luents through finely granular adsorptive and oxidative coal filter medium contained in said smaller filter section.

3. A method as claimed in Claim 1. in which the adsorp-tive and oxidative coal filter media is segregated according to their known adsorptive properties and in a predetermined range of specific filter media sizings by means of baffles, dividers or pervious containers.

4. A method as claimed in Claims 1, 2, or 3, wherein the filtered septic tank effluents discharged from the filter-bed smaller filter section into the lar-ger filter section, wherein the said septic tank eff-luents are passed through the segregated adsorptive and oxidative coal filtermedia in predetermined spec-ifically sized aggregations thereof in the direction of from the coarser coal filter media to the finer coal filter media, and thereafter discharging the tertiary treated septic tank effluents from the said filter bed through said screened outlet means.

5. In the method of removing contaminants from septic tank effluents wherein the said effluents are passed into and through the adsorptive and oxidative finely granulated coal filter medium in the smaller filter section of the filter bed and then into and through the segregated coarse to finely granulated adsorpt-tive and oxidative coal filter medium in the larger filter section of the filter bed, then terminating the procedure when a backpressure develops to prevent the effluent flow through the said coal filter-medium to a predetermined degree, then passing backwash water through the said adsorptive and oxidative coal filter medium in the said smaller and the said larger filter sections in the direction opposite to the normal eff-luent filter flow pattern, and then passing the said backwash water and dislodged sludge through said back-wash conduit means to the said septic tank inlet means and discharging it therein.

6. A method as claimed in Claim 4, wherein the dischar-ging tertiary-treated septic-tank-effluents from the aforesaid adsorptive and oxidative coal-containing filter bed are discharged into an effluent dispersal field comprising conventional baked-clay sewage drain-age tile or conventional perforated plastic sewage drainage pipe laid within the aforefiaid adsorptive and oxidative coal pervious distribution medium, where-in the said tertiary treated effluent from said filter bed is dispersed from said drainage tile or drainage pipe through said pervious distribution medium to main-tain said effluent at an acceptable standard of tertiary-treatment effluent quality suitable for discharge to surface waters.

7. A method as claimed in Claim 4, wherein the discharg-ing tertiary-treated septic-tank effluents from the aforesaid adsorptive and oxidative coal-containing filter bed are discharged into an interim sewage coll-ection and distribution leach line in which convent-ional perforated plastic sewage drainage pipe is laid within adsorptive and oxidative coal pervious dist-ribution medium, wherein the said tertiary-treated effluent from said filter bed is dispersed from said interim sewage collection and distribution leach line into and through said pervious distribution medium to maintain said effluent at an acceptable standard of tertiary-treatment effluent quality suitable for discharge to surface waters.

8. A method as claimed in Claim 4 wherein odour control is maintained in the septic tank filter beds by keeping the liquid effluent level within the adsorptive and oxidative coal filter medium of the said filter beds at least 4 inches below that of the top of the said coal filter medium placed horizontally in the said septic tank effluent filter bed.