Opportunities for decentralized treatment, sewer mining and effluent re-use

ELSEVIER Desalination 106 (I 996) 273-283

DESALINATION

Opportunities for decentralized treatment, sewer mining and effluent re-use

Rhett Butler*, Tony MacCormick

Memtec Limited, Locked Mail Bag No. 1, Windsor NSW, 2756 Australia

Tel. +61 (4) 577-0915; +61 (4) 587-7126

Received 23 May 1995; Accepted 29 August 1995

Abstract

The environmental need for re-use is obvious. Technology already exists, or is being developed, to make this happen more reliably and economically. Membrane technology is now validated for large-scale municipal wastewaters. To date re-use has been constrained by unfavourable economics. This, in large measure, is because so much of the treatment infrastructure is invested in non-adding value pipes in the ground, storage and disposal. Decentralized treatment is the vehicle for converting non-adding value investment into advanced treatment making wastewater re-use more economically viable. This is achieved using advanced membrane solutions such as microfiltration and reverse osmosis technologies. As in the computer industry where laptops have placed power in the hands of the user, so decentralized treatment will open up opportunities for re-use hitherto believed impossible. Authorities can speed this evolution by changing regulatory requirements which concurrently insist on higher standards of discharge and encourage re-use and decentralized treatment of effluent.

Keywords: Wastewater re-use; Microfiltration; Reverse osmosis; Decentralized treatment; Sewer mining

1. Introduction

This paper examines the opportunities available for industrial and municipal effluent re-use and reclamation as well as addressing the issue of “product differentiation”. The issue of industrial urban water re-use has been addressed in the context of decentralized water and wastewater treatment. Catchment management practices

*Corresponding author.

dictate that the Australasian water and wastewater industry, in conjunction with other indus- tries, must deliver a more effective system for effluent treatment (water use). The wider issue of re-use and reclamation must be evaluated on both economic, social and environmental grounds as suggested by Beder [ 11.

The latest developments in re-use technology such as mains interception sewage treatment (MIST) are already in evidence with projects such as the ACTEW Southwell Park Water Min- ing Project. This has been put in context with

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274 R. Butler. T. MacCormick / Desalination 106 (1996) 273-283

their removal and treatment capability and rela- tive cost. The notion of an incremental “tiered” philosophy to water re-use has been proposed, as well as the overall interaction with urban water cycle. Real opportunities will be available to private sector and public sector schemes which address the “higher tier” applications currently available in the industrial and non-potable sec- tors.

The cost of re-use is perceived to be relatively high. However, the existing projects such as the Pacific Power re-use project described later indi- cate unit costs are comparable with the combined costs of water supply and discharge. Overseas experience, particularly within the southeast and southwest regions of North America, illustrates that advanced wastewater re-use/reclamation plants such as the Water Factory 21 demonstration project or Reedy Creek Demonstration [Z] described herein are technically, economically and socially viable.

There will be increasing opportunities for collaborative ventures among and between industry and public sector waste authorities. Perhaps the greatest opportunities for infrastructure and development and re-use vest in the dynamic industrial centres of Australia and Southeast Asia in the next 20 years. Re-use of industrial effluent will be a major component of the overall busi- ness opportunities.

Southeast Asia industrial centres present the best opportunities for advanced wastewater treatment technologies. Clearly, the issue of wastewater treatment has two dimensions - municipal and industrial. Based on Australian and US expe- riences, the two will become synonymous. That is, wastewaters may become a tradable commodi- ty. Sewage effluent, for example, is an excellent source for process water supply. The real issue is that water, whether it be effluent or potable water, is a differentiated product. This is a fact.

The real opportunity and incentive for “new players” in water re-use and reclamation is the economic necessity to harness municipal wastewaters. Under the current centralized design and operation of our water and wastewater networks,

it is indeed very difficult to obtain an economically acceptable return on investment [3]. There- fore, a new approach which incorporates advanced wastewater process philosophy and an integrated catchment management philosophy is a potential niche. Municipal water reclamation projects such as groundwater and aquifer re- charge are economically viable in the US. There are niche areas for immediate participation in advanced water and wastewater reclamation projects. The greater Bangkok metropolitan region is a prime example.

2. Current re-use practices and drivers in Australia

Wastewater recycling in Australia currently comprises less than 10% of water used for urban and industrial purpose [4]. Most applications in- volve agricultural and landscape irrigation. The schemes exist as much to avoid discharging effluent into inland rivers as they do to use a scarce resource. Treatment is minimal, seldom better than secondary treatment with various levels of chlorine disinfection. Re-use in urban environments where most of the effluent is gen- erated remains small.

TabIe 1 summarizes the treatment processes encountered in municipal sewage treatment and shows the level of treatment typically applied to various disposal and re-use options.

Throughout this paper it is assumed that the starting point for re-use is a 20/20 nitrified secondary treated effluent without significant nutrient removal or disinfection. This is the minimum level of treatment usually specified for near shore disposal or disposal to land where there is no risk to existing groundwaters.

Table, 2 looks at the categories of reclaimed

water reuse (secondary effluent that has under- gone further treatment) and the primary contaminant removal for each category.

2.1. The arguments against re-use tf efluent

The arguments against re-use are primarily

R. Butler, T. MacCormick / Desalination IO6 (1996) 273-283 275

Table 1 Typical sewage treatment for various disposal and re-use options

Disposal Primary Secondary Nutrient Clarification Full Reverse Sludge removal and filtration disinfection osmosis handling

Deep ocean . .

Near shore l . .

To sensitive waterways l . . . .

Agricultural re-use l . . .

Unrestricted urban re-use l l . . .

Indirect potable re-use l l . . . . .

Table 2 Contaminant removal for alternative re-use strategies

Re-use strategies Contaminants to remove

Disinfection and monitoring

Agriculture and woodlots l

Urban irrigation . .

Dual reticulation &..

Industrial water . .

Indirect potable . . .

Suspended solids and algae

.

.*

. . .

. .

. . .

Dissoived phosphorous

. . . I..

Other TDS (organic and inorganic)

Limits on salts

Limits on salts . . .

Low l Minimal ponding Good settling lo-15% removed N/A with solids

Medium l * Chlorine or UV Sand filtration BNR or equiva- N/A lent, 70% removal

High l ** Chlorine and fre- Coagulation and Chemical “P” Activated carbon quent monitoring or media filtration or removat or mem- and/or membrane membrane filtration membrane filtration brane separation separation

economic but also include technical and community attitude issues. Adverse community attitudes towards re-use are doubtful. Wherever authorities have introduced re-use schemes with appropriate quality controls and consultation, community support has been positive. Highly treated wastewater has been injected back into the fresh water aquifer supplying Los Angeles since 1976. In Australia a workshop organized by concerned residents for the township of Landsborough just north of Brisbane is an interesting case in point.

Table 3 shows how the meeting rated four alternative sewage strategies against previously agreed criteria. It was interesting to note that far greater importance was given to environmental criteria than to impact on rates or job creation.

Technical concerns usually relate to the capacity of treatment to remove human pathogens reliably. The argument is that microbial quality can be maintained from large plants that are manned around the clock but not guaranteed from small unmanned plants. While membrane

276 R. Butler, T. MacCmnick ! Desalination 106 (1996) 273-283

Table 3 450

A community view of sewage treatment priorities

Criteria selected to assess alternative sewage strategies

Criteria Score out of 10

Actual risk to community health 9.5 Impact on receiving water or land 6.8 Water conservation 10 Impact on rates 2.7 Potential job creation 3.6 Proven reliability 8.2 Flexibility (change and expansion) 4.5

How sewage strategies rated when scored against selection criteria

,gJj ‘_ . . _.

:/

.- .._....... .._. 1 . +_. ,,........ _._._._._ . . . ..__. j”. ., ,.,....._...,..... _

--m-i Potable saving Ct 600 L/day

100 L I. L I .

50 100 150 200 Price of potable water - cents/KL

Fig. 1. Price of water for re-use break even.

Treatment strategy

Discharge to river after secondary treatment

Score

34

Discharge to land after nutrient removal

4.5

Discharge to land for agricultural re-use

83

Recycle to houses as non-potable water

123

Source: Landsborough Workshop, July 1994.

technologies can overcome reliability concerns, the fact remains that the potential savings do not appear to justify the additional cost of treatment either to a potable standard for indirect re-use or for the cost of dual reticulation for non-potable re-use.

Water -w TOtsI

I3 Treatment 0 Reticulation, siomge 8 disposal

Fig. 2. Cost of new urban infrastructure.

to existing potable raw water storage but before concentrate disposal is taken as $1.27/KL.

Figs 1 and 2 show the economic argument graphically. As can be seen from Fig. 1, both the cost of treatment to a potable standard and additional non-potable reticulation - especially if retrofitted in an existing urban environment - cannot be recovered unless the cost of water is twice the current rate of 40 to 70 cents/KL. The calculation assumes the incremental cost of treatment, storage and reticulation to an urban re-use standard is $2,900/1ot. The cost of the extra reticulation is amortized at 8% over 30 y. Treatment to potable standard including mains distribution

Fig. 2 shows the cost of water and wastewater infrastructure for a new urban development. It is important to recognize that the cost of treatment is less than half the non-adding value cost of reticulation, storage and disposal. Clearly one way of improving the cost effectiveness of infrastructure is to reverse this ratio. This is discussed later.

There is little doubt that environmental pressures to conserve water and improve discharge standards will increase the pressures to re-use. Technology will make this trend happen more

R. Butler, T. MacCormick / Desalination 106 (1996) 273-283 277

quickly. The economic pay-off will occur if we can find ways of reducing the huge non-adding value cost of reticulation. This will require decentralized treatment - treatment which removes more contaminants at lower cost and more reliably than currently available.

2.2. Reliable jiltration and disinfection is para- mount in re-use

While there is a range of parameters that must be controlled in recycled water, the principal concern of authorities in western cities is microbiological control of pathogenic bacteria, parasites (protozoa and helminths) and viruses. Very tight control over these pathogens is particularly important if the reclaimed water is destined for unrestricted non-potable re-use, i.e., where there is risk of people coming into direct contact with the water such as mist from irrigation spray.

Protozoa, particularly giardia and cryptosporidium* must be removed by reliable filtration as they are unaffected by chlorine. Sand, diatoma- ceous earth and other multi-media filtration tech- niques achieve filtration by trapping particles within the media bed itself. Protozoa are large enough to be trapped in this manner. The small- est particles, such as viruses and bacteria, pass through. Further, as filtration proceeds, the bed becomes filled with the removed contaminants and under certain circumstances can shed leading to unexpected sharp peaks in contamination downstream of the filter. While a sand filter can remove a proportion of the microbiological contaminants, it cannot do so completely, nor is it entirely reliable.

It is for this reason that conventional filtration processes rely on chlorination or UV sterilization to achieve disinfection of bacteria and viruses.

While both these processes are effective, their efficacy can be impaired significantly by the presence of solids (caused, for example, by filter shedding) which shield the microbiological or- ganisms from the full effect of the chlorine or UV light. The effectiveness of chlorine and UV is thus extremely dependent upon the efficiency of the filtration system.

As mentioned, membranes differ from sand and other media filters by physically preventing solid particles, including pathogens, from pene- trating and passing through the filtration membrane. By and large this occurs because the particles are larger than the pore size of the membrane. This characteristic allows the filtration process itself to disinfect. With redundant chlorination or UV, membranes facilitate double disinfection.

Unlike all other filtration systems used in effluent polishing, Memtec’s continuous microfiltration (CMF) ** has the capacity to self-monitor its own integrity. This allows real-time testing of system integrity, advance notice of a possible problem and less frequent and costly microbiological sampling and analysis.

It is this capacity to guarantee particle rejec- tion above a certain size that allows membrane technologies to be a backdrop to upstream processes. They provide a guarantee of process control not normally available with conventional separation processes and open up the prospect of treatment to a re-use standard on a small scale in plants run unattended and controlled remotely. The implications of this are a substantial drop in the cost of reticulation. CMF systems also come equipped with data loggers which can be used to interpolate the performance of upstream processes as well as monitor the microfiltration process itself.

*Giardia and cryptosporidium are a growing cause of water-borne illness worldwide. The US Safe Drinking Water Act is in large measure designed to ensure removal of these parasites. They are not inactivated by chlorine and must be removed by reliable filtration. **Continuous microfiltration is the patented technology of Memtec Limited (“Memtec”).

278 R. Butler, T. MacCormick /Desalination 106 (1996) 273-283

3. Tighter requirements for discharge to the environment

Environmental protection authorities throughout the world, and particularly in western coun- tries, are gaining and implementing greater regulatory power. In Australia the Victorian EPA is the most active. The US EPA has wide legal power and a budget that has allowed it to estab- lish far-reaching standards based on up-to-date research. The consequences of privatizing the UK water industry has given the National Rivers Authority and other regulatory authorities in the UK greater independence from political interfer- ence as well as increased regulatory powers.

Having extricated itself from the provision of water and sewage services, the Government now focuses on improving the quality and standards for these services. They are now in a position to take the political credit for tightening water quality and discharge standards without having to bear directly the cost of these policies.

In industry the term “zero discharge policy” is heard more frequently. Many companies are showing that wastes can be reprocessed, recycled, and contained on-site without environmental damage - often with savings that offset the incremental cost. Memtec have long argued that setting higher standards forces technical innovation with cost and environmental benefits ulti- mately flowing to all. Certainly, tighter regula- tions cannot be applied overnight, and in some cases 5 y will be necessary.

Some interesting examples of technical innovation resulting from tighter discharge requirements are as follows:

a quality better than potable water. Reverse osmosis (RO), the final membrane process, is used to remove dissolved ions, while microfiltration is used as the RO pretreatment. It provides the backstop to the biological process as explained earlier in this paper. l Welsh Water, UK - The European Union guideline for bathing waters incorporates a faecal coliform level of 400 cfus/lOO ml in 90% of samples. Populations of -40,000 discharging to the sea generally do not require secondary treatment under the EU European Wastewater Treat- ment Directive. However, where the discharge could influence the quality of bathing water, it requires disinfection under the Bathing Water Directive. This has allowed Dwr Cymru Welsh Water the option to filter a primary effluent as a means of removing suspended solids and provid- ing disinfection without resorting to secondary treatment, filtration and UV (chlorination of secondary effluents for ocean discharge as in New Zealand is discouraged). . A major nickel refinery - Although not a municipal effluent, an interesting example of economic re-use is found in a minerals processing plant. Liquid waste from a nickel refinery is currently contained in a large tailings dam. The waste contains significant levels of ammonium sulphate. The combining of nanofiltration and RO can recover the ammonium sulphate and low pressure boiler quality water, both of which are recycled to the refinery process. Microfiltration is used as a pretreatment for the nanofilter as the latter fouls rapidly from algae in the tailings pond.

l APM New Mexico - Australian Paper Manu- 9 ACT Electricity and Water - ACTEW have facturers have installed a new paper recycling coined the words “water mining” to describe the

plant in New Mexico in the US which contains process of extracting raw sewage from a sewer and treats all liquid effluent on site. APM are main and treating it to a standard suitable for world leaders in the recycling of waste paper and irrigating open access public space. The concept are setting new standards for the re-use of waste- behind this process (Fig. 3) is to increase the util- water used in this process. They are combining ization of existing sewage collection and treat- biological treatment with two membrane process- ment infrastructure and to delay the construction es to treat the wastewater for recycling back to of new dams for potable water by reusing treated the process and as boiler make-up. The latter has municipal wastewater. The plant is compact,

R. Butler, T. MucCormick ! Desalination IO6 (1996) 273-283 279

PlillM~ BbforblologkEal trealment reactm

Odour : . . . . . . . . . . . . . . . . ..I.-.........- *..-I***..* .._-------.._.__. _ . .._ +

t ! I

! :

. . . . . . . . . . . . control

extmcbon Fig. 3. The ACTEW water mining

Fig. 4. Microfiltration replaces a complex six-step RO pretreatment train at Water Factory 21.

housed in an odour controlled building and occu-

pies a land area of only 180 m2. It has a capacity of 0.6 mlpd. The process involves raw sewage extraction, chemically assisted primary treatment, biological treatment in a Biofor fixed film bio- reactor (supplied by Sepa Waste Water Treatment

Pty Ltd.) and microfiltration and chlorination to provide double disinfection. The plant is designed to operate unattended and will be controlled remotely from the Lower Molonglo treatment plant.

l The Rouse Hill Development - Located in

280 R. Butler, T. MacCormick / Desalination 106 (I996) 273-283

northwest Sydney, it comprises a sewage infrastructure to service 300,000 people by the year 2017. Water conservation and wastewater discharge are major issues in the Hawkesbury Nepean system. The government has decided the development will include dual reticulation for domestic non-potable uses such as toilet flushing and garden watering and extensive effluent re-use of open spaces, forests and in industrial areas. The treatment plant uses advanced biological processes, conventional coagulation/multi-media filtration and chlorine disinfection to achieve the re-use standard. The project will re-use around 45% of treated effluent from urban development. l Water Factory 21 - Since the early 1970s Water Factory 21 of Orange County Water Dis- trict has been treating secondary effluent to a potable standard for recharging a fresh water aquifer. The aquifer, which is a major source of potable water for the Los Angeles area, has dropped significantly over the years and is sub- ject to salt water ingress. The existing plant includes a six-step lime-based pretreatment process to remove fine solids, bacteria and viruses ahead of RO (Fig. 4). Since April 1992, as part of a strategy to double the plant’s capacity, Water Factory 21 has been testing one-step microfiltration to replace the existing expensive and opera- tionally troublesome pretreatment. The work has produced such favourable results that the district is now installing a 2.7 mlpd microfiltration system as part of its scale-up strategy. The plant will demonstrate the technical and economic benefits of microfiltration as an RO pretreatment, not only at Water Factory 21, but also in several other LA recycling projects which in total have the potential to recycle up to 375 mlpd of municipal wastewater.

4. Drivers working in tandem to encourage re-use

The final section of this paper covers an existing industrial project and a new residential concept where environmental imperatives and techni-

cal innovation are making the re-use of treated secondary effluent economically viable.

l Pacific Power - This project is a major re- use initiative at the NSW Eraring Power Station. The Hunter Water Corporation is currently under- taking a major provision of sewage services to communities on the southwestern side of Lake Macquarie. The project includes a 6,000 EP wastewater treatment plant at Dora Creek, a few kilometres south of Eraring. Originally it was intended to pump secondary effluent under Lake Macquarie to an extended outfall at Belmont. The re-use project involves taking secondary effluent from the Dora Creek Plant, on-site treatment at Eraring and re-use to reduce significantly the station’s requirement for fresh water (Fig, 5).

The project will delay the extended outfall project for at least 15 y. The 15 km of effluent pipeline not built will save Hunter Water Corpo- ration $2.7 million. Another $2.3 million will be saved by the NSW State Government and will allow further augmentation of sewage works in the west lake region.

The project demonstrates the synergistic benefits of using membrane technologies in series. RO is a desalination technology widely used to reduce dissolved solids in wastewaters. It per- forms poorly, however, on feedstreams with even low levels of either suspended solids or bacteria. These contaminants can rapidly foul the RO membrane, often irretrievably. In comparison, microfiltration is a highly efficient process for removing suspended solids down to the level of detection but is a poor remover of dissolved solids. The Eraring project combines these technologies. Microfiltration provides the high level of pretreatment required by RO improving the cost and reliability of the second membrane system dramatically. l Residential on-site treatment - The final example involves on-site treatment (at a residential level), collection of the liquid effluent gener- ated, central treatment of this effluent and recycling for safe urban re-use. This concept assumes that on-site treatment systems exist or can be


Hunter Sewage Project n mweststdeof LakeMaapar& n Bu#a16,OOOEPSTPatDoraCre& n oumlurulerLakeMecqualietoBemont

ReusepmjectwlH n Lk&4y4xumdedoutfellIbrl5years

Y

/

n Save Hunter Water Cwp andeState Gowmment UmtNon

I Fig. 5. Pacific Power sewage re-use project.

Fig. 6. On-site treatment with overflow collection, treatment and recycling.

developed to produce consistently a 20/20 effluent or better. If so, the liquid effluent produced can be collected in a low pressure polypipe sys- tern at one-third the cost of conventional gravity collection which must be sized for both liquids and solids. With appropriate buffer storage, aug- mented by storm water runoff, almost all the

treated sewage effluent can be recycled reducing significantly the size of the potable water infrastructure and demand. The concept is shown in Fig. 6.

Capital and operating cost estimates for an integrated water and wastewater infrastructure incorporating these concepts suggest a net present

282 R. Butler, T. MacCormick / Desalination I06 (1996) 273-283

Table 4

The economics of on-site treatment and recycling

Infrastructure capital cost for a 5O(rlOOO lot development

cost, $/lot Reasons for difference, assumptions and comments

Existing On-site, Difference approach dual supply

Water treatment plant, pump station, rising main and reticulation

3,575

Sewage collection, pump station and rising main

5,000

Sewage treatment plant including nutrient removal

2,500

Land disposal system

Wetland and buffer storage; no land disposal

230

N/A

Non-potable treatment plant N/A

Non-potable storage, pump station, rising main and reticulation

Total

Available for on-site sewage treatment

N/A

11,305 77420

N/A 3,855

% of cost in treatment 30

2,130

1,545

370

1,000

2,375

47

(1,445)

(3,455)

(2,500)

( 230)

370

1,000

2.375

(3,885)

0

Dual system allows the plant and infrastructure to be sized for potable demand only

On-site 15120 treatment allows sewage collection in a small bore low pressure system

Simple pond system without nutrient removal could be as low as $1000 per lot

Cost of land and irrigation system

Cost of land and storage construction for 20120 effluent from on-site treatment

Filtration and disinfection to NSW urban re-use guidelines

Sized for peak external water use and fire fighting

Some on-site treatment systems (without disinfection) are available close to this cost

value saving of up to 30% over conventional systems of sewage collection and treatment for communities of up to 3,000 people. These estimates assume on-site treatment at a capital cost between $3,000-4,000 per house compared to a conventional centralized system for a similarly sized community required to meet advanced nutrient removal (Table 4).

One on-site treatment system showing consid- erable potential is based on the combination of vermiculture (worms) technology with conventional aerobic treatment. The system is odour free, appears resilient to all normal household waste including nappy disinfectants and dish- washing detergents and has the added attraction of being able to consume all putrescible garbage.

The above concept is environmentally appeal-

ing. It involves natural biological and filtration processes to recycle solid and liquid waste safely and appears to have an application in new residential communities or existing communities requiring conversion from septic or pump out to centralized sewage collection.

The above two examples have a number of factors in common. First, they incorporate high levels of treatment necessitated by tighter environmental requirements. Second, they allow previously wastewaters to be recycled through a combination of technologies, frequently membrane based, saving significant quantities of fresh water. Third, they are all decentralized; costs previously associated with non-adding value “pipes in the ground” are redirected towards more advanced treatment.


References

[I] S. Beder, Pipelines and paradigms - the development of sewage engineering, Institution of Engineers Australia, Civil Engineering Transac- tion Paper, 35 (1993).

[2] J. Lozier, D. Bedford, B. FuIgham and H.R. Kohl, Evaluating reverse osmosis membrane performance on secondary effluent pretreated by

membrane filtration - a report on the Reedy Creek Energy Services Water Treatment Plant Project, AWWA Conference, San Antonio, 1993.

[3] Industry Commission of Australia, Report on the water industry, ICA, Canberra, 1990.

[4] J.M. Anderson, The potential for water recycling in Australia - expanding our horizons. Paper given at the AWWA Mini-symposium, Perth.

Opportunities for decentralized treatment, sewer mining and effluent re-use

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