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War. Sci. Tech. Vol. 32, No.3, pp. 317-327,1995.Copyright@ 19951AWQ

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REED BED TREATMENT SYSTEMS FORSEWAGE TREATMENT IN THE UNITEDKINGDOM - THE FIRST 10 YEARS'EXPERIENCE

P. Cooper* and B. Green**

* WRc pic, Frankland Road, Swindon, Wiltshire, SN5 8YF. UK** Severn Trent Water Development Group, Coventry, UK

ABSTRACT

The UK Water Industry first became interested in Reed Bed Treatment Systems for sewage in 1985. Earlyproblems were experienced with soil-based horizontal-flow systems of the Root Zone type. The problemswere overcome by national co-ordination of a development programme and international co-operation by anEC Expert Contact Group. A number of different types of systems have now been developed and the systemsare now being accepted. The paper reviews the development of these systems for secondary and tertiarytreatment and nitrification and mentions development of systems for other forms of treatment. The designchanges made to overcome the problems are described. These include the gradual move to the use of gravel­based systems because of the difficulty experienced with over-land flow in the soil systems. The sizing of thesystems is described together with performance data for the original horizontal-flow and the more recentlydeveloped vertical-now systems. Treatment at secondary and tertiary levels is illustrated and the potential fornitrification. Early problems with reed growth have been overcome by planting with port-grown seedlings.

After 10 years the process is generally accepted by the Water Industry as an appropriate treatment forvillages and there are now between 200 and 300 systems in operation.

KEYWORDS

Design guidelines; flow distribution; horizontal-flow systems; media; nitrification; Phragmites australis;planting; reed bed treatment systems; secondary treatment; sewage treatment; small communities; smallsewage treatment works; storm sewage overflows; tertiary treatment; vertical-flow systems.

INTRODUCTION

The UK Water Industry first became interested in Reed Bed Treatment System (RBTS) in 1985 followinginformation on systems that had been built in Germany and Denmark, (Boon, 1985). These so-called RootZone Method (RZM) treatment systems were horizontal-flow systems. A visit to Germany was arranged andit was clear that the process had some potential for small-scale rural treatment. However, it also becameclear that some of these systems had failed, in many cases because of surface flows and scouring. It wasdecided in late 1985 that it would be beneficial for the UK Water Companies to co-operate and exchangeideas to avoid the repetition of faults that had occurred in Germany and Denmark. The Water ServicesAssociation is the UK Water Industry body which provides a national forum and so it was decided to form aReed Bed Treatment Systems Co-ordinating Group under its auspices. The group set itself a 5 year research

317

318 P. COOPER and B. GREEN

and development programme with the ultimate output being a set of Guidelines on RBTS. WRc acted as theco-ordinator of the programme. On behalf of the group, WRc also contracted out pieces of research intoareas which were outside the expertise of the Water Industry. A good example of this was the programme ofwork carried out by the Institute of Terrestrial Ecology (ITE) who evaluated the different methods ofpropagating and planting reeds and showed how to grow from seeds from native British Phragmitesaustralis which had been said to be infertile. In late 1985 the group started to exchange experiences withworkers in Germany and Denmark. This led, in 1986, to the formation of a European Community ExpertContact Group on Emergent Hydrophyte Treatment System (EHTS). The national groups in nine ECcountries funnelled their information through to the European Group. WRc acted as the Secretariat and Co­ordinator of the Group. Meetings were held at six monthly intervals to allow the information to be passedfreely between the countries. The culmination of the work of the group was the organisation of anInternational Conference on Constructed Wetlands at Cambridge in September 1990 at which the Grouppresented its European Design and Operations Guidelines for Reed Bed Treatment Systems (EC/EWPCA,1990). These guidelines concentrated on horizontal-flow systems but mentioned the potential of the vertical­flow systems which were then starting to be developed.

From 1990, in the UK there has been no co-ordination of research and development since the industryregarded the systems as a relatively mature technology. From that point on, there has been gradualimplementation of the technology and the process has spread outside the Water Industry to areas such asfarm waste treatment, landfill leachate treatment, single house and caravan/campsite treatment. Many smallentrepreneurs have started to develop new systems and implement the older systems especially for smallcommunities. The precise number of systems being used is not known since the end of the steering group in1990, but it is likely that there are between 200 and 300 systems in operation.

Seven Trent Water alone had 102 systems in June 1994 (Green and Upton, 1994). They have many systemsfor storm sewage treatment and for the tertiary treatment of existing sewage treatment plant effluents. Alltypes of constructed wetland are represented in the UK; sub-surface flow systems (horizontal-flow systems,vertical-flow systems, hybrid systems), surface flow systems and even some pond systems.

THE PRESENT SITUATION

When the UK Water Industry first became involved with RBTs in 1985 it was with horizontal-flow systemswhich had soil as the media. Some of the basic design principles put forward by the developers of the RootZone Method (RZM) systems have proved to be correct but many of them have been shown to be wrong orinadequate descriptions of the physical situation. Over the decade the specific design features have beentested and gradually developed. There has been a gradual devolution towards vertical-flow systems. This isprimarily because the horizontal-flow systems of the RZM-type are oxygen-limited and cannot achieve fullnitrification (or even full BOD removal because of oxygen limitation). Quite early on it was pointed out byKlaus Bucksteeg, the German representative on the EC Group, that RBTS are crude rustic biological filters(Bucksteeg, 1987). They are shallow biofilters and because they are shallow they need a larger surfacearea/pe than do conventional biofilters. At the start of the decade much was made of the ability ofPhragmites to transfer oxygen. This was proven by Armstrong et al.(l990) and Brix and Schierup (1990) butthe oxygen flux was not fully defined and we tend now to think that it is not a significant fraction of theoxygen demand. Because of the inability to supply sufficient oxygen through the reeds there has been agradually increasing interest in vertical-flow systems where oxygen transfer (by entrapment in anintermittently-dosed bed) was known to be much higher.

At the start of the decade the UK Water Industry saw RBTs as methods for achieving secondary treatmentfor sewage treatment plants (up to 2000 pel for achieving effluent standards for BOD and TSS of typically20/30 mg/l. Their use has now expanded into the following areas:

(i) to achieve ammonia removal (by oxidation) to standards < 5 mg NH4-Nn vertical flow systems only;

Reed bed treatment systems 319

(ii) tertiary treatment of secondary effluents from biological filters or RBCs. Mainly SS removal but thismay include nitrification;

(iii) storm sewage treatment;

(iv) treatment of sewage from sites without sewers e.g. hotels in remote locations, caravan sites; touristsites (Hudson, 1994; Grant, 1994);

and outside the UK Water Industry.

(i) treatment of animal waste from farms;

(ii) landfill leachate treatment

There are now very many different variants but it is probably fair to summarise the situations as follows.

There are more horizontal-flow systems than vertical-flow by a ratio of probably 4 or 5:1.

Horizontal-flow systems (HFS) are seen as suitable for the following situations.

(a) Secondary treatment where BOD and TSS to about 20/30 BODITSS is required but nitrification willnot be achieved. A good example of this would be the system designed by WRc for Severn TrentWater at Little Stretton - July 1987. (See Table 1).

(b) For tertiary treatment where the aim is to remove SS (and hence some BOD). Figure 1 shows theeffluent quality achieved at 42 sites in Severn Trent Water.

Table 1. Performance data for Little Stretton secondary treatment horizontal-flow RBTS since July 1987

BOD (mg/l) TSS (mg/l) NH4N (mg/l) TON (rng/l)In Out In Out In Out In Out

1987 147 29 132 19 10.0 10.0 15.0 1.01988 112 33 85 24 12.2 13.8 12.2 3.41989 162 34 127 43 14.9 11.3 9.1 3.01990 112 3.9 93 28 24.8 12.1 2.2 6.21991 55 4.1 70 28 14.7 5.9 9.0 6.21992 26 1.7 41 22 8.0 0.4 22.2 16.61993 35 1.7 30 8 8.4 0.2 11.4 1.6

Vertical-flow systems (VFS) are also seen as being better for achieving effluents which have oxidisedammonia-N to nitrate as well as doing BOD removal.

320 P. COOPER and B. GREEN

mgtl5-,-----,-------------------------,

.BOD4 _ .

3

2

1

'0 Effluent BOD data

mgtl7

.SS6

5

4

3

2

1

, b Effluent 55 data

mgtl

• amm NB-,--- - ----,-------------- - ---------,

6

4 .

'C Effluent arnrnonia-N data

Figure I. Annual mean effluent data from 42 tertiary RBTS in Severn Trent Water.

Reed bed treatment systems 321

The first of these systems was designed by Uwe Burka of Camphill Village Trust at Oaldands Park,Gloucestershire (Burka and Lawrence, 1990) in 1989. See Table 2.

Table 2. Performance data for Oaklands Park secondary treatment RBTS - August 1989 to September 1991

Influent Stage I Stage II Stage III Stage IV Stage V

BODs (mg/l) 258 57 14 15 7 IITSS (mg/l) 169 53 17 11 9 21NH4-N (mg/l) 50.5 29.2 14.0 15.4 11.1 8.1TON (mg/l) 1.7 10.2 22.5 10.0 7.2 2.3Ortho-P (mg/l) 22.7 18.3 16.9 14.5 11.9 11.2

STAGES I & II are vertical flow; STAGES III& IV are horizontal flow; STAGE V is a pond

In April 1993 WRc installed a vertical-flow system for the Medmenham site to achieve BOD removal andnitrification of a poor effluent from an old biological filter. Table 3 summarises the performance of thissystem for the first year.

Table 3. Performance of the vertical-flow beds at WRc Medmenham

14/5/93 - 29/10/93 BODs mg/l TSS mg/l NH4·Nmg/l

Biofilter effluent (11 samples) 16.6 16.5 6.6Reed bed 1 effl. (23 samples) 5.6 5.3 1.7Reed bed 2 em. (23 samples) 6.1 6.0 1.8

15/4/94 - In/94 BODs mg/l TSS mg/l NH4·Nmg/l

Biofilter effluent (10 samples) 27.4 34.4 7.1Reed bed 1 em. (10 samples) 9.6 10.1 2.7Reed bed 2 effl. (10 samples) 4.6 9.8 1.4

Hybrid systems

There are advantages in combining HFS and VFS in that the VF system will be good at removing NH4N andBOD and HFS is good for SS removal. HFS are also potentially useful in removing nitrate by biologicaldenitrification (under anoxic or anaerobic conditions). This can be seen for the Oaklands Park system (inTable 2) when the NH4-N is converted to nitrate-N and nitrite-N in the VF stages I, II and then graduallyreduced by denitrification in the HF stages III and IV.

The European Design and Operations Guidelines on RBTS were produced in December 1990 and haveserved the UK Water Industry very well but they had a number of weaknesses which now need rectifyingbecause more up to date information exists. For example:

322 P. COOPERand B. GREEN

(i) there was little information available in 1990 on VF systems and so the design advice was verylimited;

(ii) there was no experience at that time on tertiary treatment systems.

In the following section we will attempt to improve this situation. Funding is still needed to produce anupdated version of the European Design Guidelines.

DESIGN FEATURES

Sizing of the systems

Horizontal-flow systems. A number of ways have been used for determining the surface area of HF systems.

(a) The "Kickuth Equation" has been quite widely used:

(1)

where

:::

surface area of bed, m2

daily average flowrate of sewage, m3/ddaily average BODs of feed, mg/lrequired daily average BODS of effluent, mg/Ia rate constant, mId

In the UK the value of KBOD used has been 0.1 for a normal strength sewage with BODs 150 to 300 mg/I.

(b) For UK conditions Ah has resulted in a value of about 5 m2/pe. In many cases systems have been sizedat this value for domestic settled sewage. Table I shows the data from the HF secondary treatmentsystem built at Little Stretton, Severn Trent Water. Little Stretton was designed by WRc using the"Kickuth equation" and then constructed by Severn Trent Water. It is a terraced HF system with 8stages and so has an element of vertical flow re-aeration between the stages.

(c) For tertiary treatment HF systems, equation (1) has been used to derive a value of I m2/pe (Green andUpton, 1994). This has been extensively used by Severn Trent Water for their many tertiarysystems. Figure I shows the data for 42 HF tertiary treatment RBTS in Severn Trent Water. Tables4 and 5 give more details of the performance of two tertiary beds. It is likely that in some cases alower value closer to 0.5 m2/pe could be adopted.

(d) Stann sewage systems. Severn Trent Water have used 0.5 m2/pe for sizing their systems or I m2/pe

when storm sewage treatment is combined in the same beds as tertiary treatment (Green, 1993).

Reed bed treatment systems 323

Table 4. Performance data for Middleton tertiary treatment horizontal-flow system since April 1987

BODs TSS NH4N TONIn Out In Out In Out In Out

1987 12.1 4.0 28.7 12.2 3.3 1.7 32.2 19.61988 7.9 2.5 24.2 13.3 2.5 0.4 29.7 16.51989 11.2 1.6 23.9 6.7 3.2 0.4 28.0 20.71990 5.7 1.9 13.9 6.5 2.7 0.2 17.6 11.41991 11.7 2.7 25.7 5.7 3.4 0.7 20.8 14.61992 8.3 1.6 19.1 4.2 2.9 0.3 17.9 11.41993 8.5 1.8 18.8 4.8 4.3 I.l 13.8 10.3

Table 5. Performance data for Leek Wootton tertiary treatment horizontal-flow system since June 1990

BODs TSS NH4N TONIn Out In Out In Out In Out

1990 9.8 4.1 18.4 5.8 6.6 4.9 34.7 23.51991 13.2 3.6 20.2 4.1 5.0 3.3 33.0 22.81992 12.8 2.3 20.7 5.0 6.1 1.9 27.2 16.41993 14.4 2.2 23.5 5.1 8.1 3.7 26.2 14.4

Vertical-flow systems.The first VF system in the UK was the Oaklands Park system built by Uwe Burka ofCamphill Water (Burka and Lawrence, 1990). It consisted of settlement, 2 VF stages followed by 2 HFstages and a pond. The performance of the system was monitored by WRc over a two year period and thedata is shown in Table 2. The area/actual pe is as follows:

Stage 1 (VF)Stage II (VF)Stage III (HF)Stage IV (HF)Stage V (pond)

0.74 m2jpe

0.23 m2jpe

0.12 m2jpe

0.31 m2jpe

1.38 m2jpe

It has become general to size VF systems a total of 1 m2jpe when using settled sewage. However as is seenfrom the Oaklands Park data - Table 2, this does not result in complete nitrification. There are still only afew VF systems. For the present time we recommend the total VF area as:

1 m2jpe for BOD removal only2 m2jpe for BOD removal followed by nitrification.

It will be necessary to split the total area into at least two stages in order to accomplish the re-aeration thatcaused by re-distribution of flows at the change from one stage to another.

In April 1993 WRc constructed a tertiary VF system for its laboratory at Medmenham (near Marlow on theRiver Thames). It takes the flow from an old inadequate biological filter treating sewage from a population

324 P. COOPER and B. GREEN

of about 200 and effluent from a fish laboratory. The 2 beds in series system was designed to remove a smallamount of BODISS but also to nitrify the effluent containing about 10 mg NH3 NIl. The performance datafor the two periods monitored is shown in Table 3. The performance of this system was affected betweenMay and July 1994 by work being above on the preceding biofilter and the settlement tanks.

The design parameters for the system were:

FlowBODsNH4·NTotal area of bedsNo. of beds 8 each

4.2 m3/h (average) 10.8 m3/h (peak)30 mgll11.5 mg/I128 m2

16 m2

Two beds are in use each day with six resting. The two beds are used in series.

HF systems in the UK tend to be 0.6 m deep at the inlet end. Some increase in depth towards the outlet.Almost all the systems built after 1986 have flat surfaces to allow for flooding to kill weeds during the firstyear of establishment.

VF systems tend to be 0.5 m deep and are made of layers of graded gravel and sand.

Cross-sectional area for HF systems has been usually determined using a form of Darcy's Law:

where

Icr dhds

cross-sectional area of the bed, m2

average flowrate of sewage, m3/s

hydraulic conductivity of the fully-developed bed. mlsslope of the bed, mlm

(2)

MEDIA

Horizontal flow beds

The advice that the UK group had from talks with Root Zone Method designers in 1985 (Boon, 1985)indicated that a fully-developed RBTS built with soil would have a hydraulic conductivity of about 3 x 10-3

mls. This has not been borne out by experience and the advice in the European Guidelines "not to assume ahydraulic conductivity of greater than that of the original media" has been followed for the UK plants builtin the past 5 years. Unfortunately at the start of the decade in 1985 several plants were built using soilmedium where it was assumed that the kf would increase. Some of these beds suffered from surface flowleading to channelling and scouring of the surface which resulted in the areas of the beds being starved ofwater and hence leading to poor reed ground. This led to by-passing and hence reduced treatment.

Because of the problems with soil, gravel started to be used from 1986/7 in beds at Gravesend (SouthernWater), and Little Stretton (Severn Trent Water) since this would allow through-flow of water from the start.It was postulated that if the gravel beds started to block with sewage solids this might be counterbalanced bythe growth of rhizomes and roots opening up the beds.

Reed bed treatment systems 325

A large number of gravel beds have now been built and the operators have been pleased with the way thatthey have performed. The oldest beds are now 7 or 8 years old. Typical gravel sizes are 3-6 mm or 5­IOmm.

In some of the systems where overland flow has occurred the performance of the bed has been adequatebecause the flow has passed through the "F Horizon" a layer of decaying reed leaves and stem debris.

One very large bed is being built by Fife Regional Council in Scotland to treat sewage from 10,000 pe. Thisbed is unusual because it is being built with a waste product, Pulverised Fuel Ash (PFA) from coal-firedelectrical power stations. This large plant was designed after extensive pilot studies and the large reed bedswill provide environmental benefits by reclaiming land.

Vertical-flow beds

All the VF systems use graded gravel as the main media in a series of layers (EC/EWPCA, 1990; Burka andLawrence, 1990) with a top layer of "washed sharp sand". These beds have performed well but some havesuffered a gradual clogging of the surface sand layer and it seems that a more careful specification of thesurface layer is needed to prevent this clogging (Hudson, 1994; Grant, 1994).

Claims have been made for phosphate removal in RBTS. This is not likely to happen with consistency unlessthe medium used is high in iron and the majority of the flow goes through the medium.

SEALING THE BED

The original advice given in 1985 was to use a plastic liner or membrane such as HDPE or Monarflex (lowdensity polyethylene with fibre reinforcement) 0.5 to 0.75 mm thick. The majority of beds built over thedecade have followed this advice and been built using Monarflex or similar but because of the expense ofthese liners (£5 to 101m2) there have been some beds built with cheaper plastic substitutes. More recently anumber of systems have been constructed using Bentonite enclosed in gee-textile. The advice given by theEuropean Guidelines was that if the hydraulic conductivity was 10-8 mls or less then it was likely that thesoil had a high clay content and could be "puddled" to provide sealing for the bed. A few systems have beenbuilt this way.

INLET FLOW DISTRmUTION

Horizontal-flow systems

The first beds in 1985/6 were constructed with vee-notch weirs but they tended to have problems withscreenable material collecting at edges and causing maldistribution. They were also expensive to constructand so there has been a tendency to move to using a single manifold pipe with adjustable tees or orificesspread along its length. These have not proved ideal either and this is one area where there is still need fordevelopment. Whichever system has been used it has been usual to distribute the flow onto a 0.5 wide areaof large graded stones, 50 to 200 mm in size, in an inlet area of the head of the bed. The large stones haveusually been held in wire-mesh gabions.

Vertical-flow systems

In these systems it is essential to get an even distribution over the whole area. Some systems have used aseries of pipes with holes or gutters to distribute the flow evenly. Another method is to completely flood thebed as part of the intermittent dosing cycle. The WRc system at Medmenham has adopted this system byintermittently pumping onto a small paved area (to prevent scouring of the surface). This has worked well.

326 P. COOPER and B. GREEN

OUTLET PIPE COLLECTOR

HQrizontal-flQw systems

This is one area where the original design advice worked well and the system has not changed much over thedecade. At the outlet end of the bed most systems have a perforated agricultural drain-pipe enclosed in a0.5 00 gabion filled with large graded stones (50-200 moo). This leads to a sump where the water level iscontrolled by a 90' swivelling elbow or a socketed pipe. In some small systems for cost saving theswivelling elbow is now replaced by a piece of flexible pipe which can be clamped in place.

Vertical-flow systems

The flow is collected by a network of agricultural drain pipes spread across the full area of the bed.

PLANTING

Almost without exception the UK beds have been planted with Phragmites.

In 1985 the original beds were planted with rhizome segments with at least one node, using advice from rootzone designers. The beds planted this way suffered from very slow development (it took the reed bed at AcleSTW, Anglian Water, 3 years to develop a good stand of reeds) and there were major problems withcompetition from weed species. Beds planted with clumps of reeds also took a long time to spread to coverthe whole bed. The UK group, through WRc, contracted the Institute of Terrestrial Ecology to study theproblem. They quickly defined how to successfully grow plants from UK reed seeds and since 1987 most ofthe beds have been planted with pot-grown seedlings at a density of 4 plants/m-. This has proved verysuccessful and a dense stand of reeds can be produced in a matter of 4 months. Severn Trent Water haveplanted reeds during every month of the year but the best time for planting has been found to be April toJune to get a good growth in the first year. Up to the beginning of June the over-wintered plants from theprevious year are used after June seedlings germinated in February. We have noticed that if the reed plantsdo not appear to be healthy and tall generally people believe that the treatment plant is not working well.The effluent quality may still be good but unless the reeds look healthy the perception of effluent quality isdifferent!

PRE-TREATMENT

Back in 1985 we started off by thinking that we could treat whole unsettled sewage in a horizontal-flow bed.We had been told that all we needed to do was screen the sewage. Problems of odour were encounteredwhen this was tried at the first RBTS plant at Acle STW (in Anglian Water). We no longer consider RBTSfor treating unsettled sewage. In almost all cases a RBTS will be preceded by a settlement tank or a septictank for secondary treatment systems.

CONCLUDING REMARKS

(i) Reed Bed Treatment Systems are now accepted in the UK as an appropriate solution for villagetreatment. They are now being installed widely.

(ii) At the start in the mid-1980's the system suffered from problems with overland flow, poor reedgrowth, maldistribution and poor BOD and ammonia removal, performance. These early failures havebeen overcome by development work by Water Companies, individual entrepreneurs, ecological(green) groups and by national co-ordination.

(iii) International and national co-operation proved to be invaluable.(iv) There has been a gradual move from using soil as the medium to using graded gravel because of the

problems experienced with over-land flow.

Reed bed treatment systems 327

(v) Because of problems with poor reed growth when planted with rhizome segments the propagation ofseedlings has been developed and has proved to be the best method of planting.

(vi) The systems are ideal for single houses and farms up to the village level; they are not cheap if properlyengineered but may still be cheaper than packaged plant.

(vii) The perception of the local residents is important. They need to be "tailored" to fit into thesurroundings. They can be landscaped to fit in with most circumstances and may produce a veryattracti ve addition.

(viii) Most systems in the UK are horizontal-flow systems. They have proved adequate for BOD and SSremoval but they have not generally removed much ammonia because they are oxygen-limited.

(ix) Vertical-flow systems have shown the capability to oxidise ammonia as well as BOD. They are stillbeing developed. They use less land than HF systems.

(x) Hybrid systems may allow for ammonia and nitrate removal.(xi) Phosphate removal has not been noted in UK RBTS to any great degree.(xii) Problems still exist. One of the areas which still needs attention is distribution especially during cold,

potentially freezing weather.

ACKNOWLEDGEMENTS

The authors wish to thank many colleagues in the UK Water Industry for supplying information on progresswith the application of Reed Bed Treatment Systems. They also wish to thank Severn Trent Water pIc andWRc pIc for permission to publish the paper. The views expressed are those of the authors alone.

REFERENCES

Armstrong, W., Armstrong, J. and Beckett, P. M. (1990). Measurement and modelling of oxygen release from roots of Phragmitesaustralis. In: Constructed Wetlands in Water Pollution Control (Adv. Wat. Pollut. Control, no. Ill, P. F. Cooper and B.C. Findlater (eds.), 41-5l.

Boon, A. G. (1985). Report on a visit by members and staff of WRc to Germany to investigate Root Zone Method for treatment ofwastewaters. WRc Report 367/S/l. Stevenage, UK. August 1985.

Brix, H. and Schierup, H. -H. (1990). Soil oxygenation in constructed reed beds: the role of macrophyte and soil-atmosphereinterface oxygen transport. In: Constructed Wetlands in Water Pollution Control (Adv. Wat. Pollut. Control, no. Ill, P. F.Cooper and B. C. Findlater (eds.), 53-66.

Bucksteeg, K. (1987). Discussion of "treatment of wastewaters in the rhizosphere of wetland plants - the root zone method". Wat.Sci. Tech., 19(7), 1063.

Burka, U. and Lawrence, P. (1990). A new community approach to wastewater treatment with higher water plants. In: ConstructedWetlands in Water Pollution Control (Adv. Wat. Pollut. Control, no. 11), P. F. Cooper and B. C. Findlater (eds.), 359.

Cooper, P. F. (1993). The use of Reed Bed Systems to treat domestic sewage: the European Design and Operations Guidelines forReed Bed Treatment Systems. In: Constructed Wetlands for Water Quality Improvement, G. Moshiri (ed.), pp. 203-217.Lewis Publishers, Boca Raton.

ECIEWPCA (1990l. European Design and Operations Guidelines for Reed Bed Treatment Systems. Presented to the conference"Constructed Wetlands in Water Pollution Control", Cambridge, UK. September 1993. Also available as WRc Report VI17, WRc Swindon, UK. December 1990.

Grant. N. (1994). Consultant. Personal communication, May 1994.Green, M. B. (1993). Growing confidence in the use of constructed reeds beds for polishing wastewater effluents. Proceedings of

Water Environment Federation. 66th Annual Conference and Exposition. General Topics, 9, 86-98.Green, M. B. and Upton, J. (1994). Constructed reed beds: A cost effective way to polish wastewater effluents for small

communities. Water Environment Research, 66(3), 188-192.Hudson, R. C. L. (1994). Cress Water. Personal communication.