Mike Mickley, Ph.D., P.E.
Mickley & Associates
Boulder, Colorado

The nature of how society and technology interact has been changing. This has been particularly evident over the past 10 years. There was a time when technological decisions were based almost entirely on economics. More recently, it has become necessary to consider the effect of technology on the physical environment. But it goes beyond this. Improved communication and information systems have led to increased awareness and with it, increased concern about decisions others make that affect our lives. A result has been increased public involvement. Complex interrelationships among cultural, societal, political, environmental, economical, and technological issues have evolved from all of these changes.

Cultural, societal, and political aspects come into play as legislators set laws and regulations, as city councils make decisions on the options available for providing drinking water, and as regulators make decisions on the permitting of plant construction and operation. The public involvement and influence in each of these areas is greater today than ever before. Decisions are not based just on technical, economic, and environmental impact considerations.

Most issues in society are now framed in this wider context and the promoting of membrane drinking water plants needs to reflect this reality. The promoting cannot be limited to the utility or city council, but must include the legislatures, the regulators, and the public.

The challenge of marketing is heightened by the fact that these groups are frequently ill-informed and carry mistaken perceptions about the nature of membrane technology. Perceptions in three general areas are discussed in the paragraphs below:

  • the role and technical performance of membrane processes
  • environmental impact and regulation of membrane concentrate
  • membrane treatment costs and water costs

Finally, the discussion addresses the need for and the approach to informing the several different groups about the nature and role of membrane technology in producing drinking water.

The tremendous growth of the membrane drinking water industry is documented in the AWWA and AWWARF publication entitled Membrane Concentrate Disposal (Mickley et al, 1993). In this work, a survey of -membrane drinking water plants above a size of 25,000 gpd provided statistical representation of the industry growth. Table 1 below shows the status of the membrane drinking water plants in the continental United States as of September, 1992.

Table 1. Number of Membrane Drinking Water Plants

All U.S.
Rest of U.S.
Brackish RO
103 (73 %)
71 (81%)
7 (58%)
25 (61%)
16 (11%)
13 (15%)
0 (0%)
3 (7%)
15 (11%)
2 (2%)
0 (0%)
13 (32%)
Seawater RO
7 (5%)
2 (2%)
5 (42%)
0 (0%)
141 (100%)
88 (100%)
12 (100%)
41 (100%)

These data are now dated. Several plants that have begun operating or are in various stages of development, were not part of the survey. This now includes ultrafiltration and microfiltration plants in addition to those types of plants identified in the survey. Figure 1 shows the steady and dramatic increase in added capacity and average capacity of brackish reverse osmosis plants for subsequent four-year periods. Most of the present capacity has been added in the last 10 years. This tremendous increases reflect the suitability of membrane technologies to solve the drinking water challenges posed by increasing populations and stricter drinking water requirements.

Historically, the reasons why membrane technology has been needed have changed. Originally, it was needed due to shortage of fresh water. Later the need was due to conservation of existing water resources. Increasingly it has been needed for cleanup of contaminated groundwater and surface water supplies (for DBCP, TCP, others). More recently, it is needed to meet the requirements of the Safe Drinking Water Act (SDWA) Amendments.

Traditional drinking water plants will continue to be used where they can produce acceptable drinking water; increasingly, however, there are situations where either:

a) the water source is a lower quality water than traditional treatment can sufficiently treat
b) traditional treatments cannot meet the SDWA amendment requirements

The value of membrane technology to produce drinking water is the quality of water produced (far better than conventional technologies and with absolute filtering capabilities) and the quality of service provided (safer and more reliable).

Membrane applications, such as desalination, are proven processes. Desalination is not in its infancy, but that is the perception because it is relatively new to drinking water, new to legislators, regulators and to the public. It is the awareness and dialogue between groups that is in its infancy. Large-scale desalination and other membrane applications have gained acceptance, and the increasing size of the plants being constructed shows the confidence that many place in membrane technology. Membranes are the technology of choice for desalting of lower quality waters, and they are leading candidates for many of the SDWA amendment applications. There is a strong need for membrane produced drinking water.

During this same time frame of rapid growth of membrane technology to produce drinking water, regulation of disposal of membrane concentrate has increased dramatically.

Many, however, are not aware of the nature of membrane concentrate and hold unfounded perceptions about it. Many are not aware of the environmental impacts of alternative technologies.

There are environmental impacts associated with any type of drinking water plant. These include:

  • site aesthetics
  • noise
  • odor and air quality
  • safety
  • disposal of residuals

For present purposes, the impacts can be considered similar for membrane and traditional plants with the exception of disposal of residuals.

Traditional drinking water plants use more treatment chemicals (both in number and amount) than do membrane plants. Because membrane processes provide a physical barrier between feedwater and product water, treatment chemicals are found in higher levels in the traditional product water than in membrane product water. Traditional drinking water plants produce a solid waste that typically is disposed of as landfill. The public has accepted this for years. Membrane plants produce a liquid concentrate that may be disposed of in several different ways. The public may not be aware of the solid waste from a traditional drinking water plant, but they frequently become aware of membrane concentrate because of the increased visibility of municipal projects and the fact that membrane concentrate is of larger volume than solid wastes and is disposed of locally. Membrane technology is new to them and not well understood. The fact that membrane concentrate is classified as an industrial waste (by regulatory definition since it is not a municipal waste containing coliform bacteria), is frequently cited as a public concern.

However, membrane concentrate is different from most industrial wastes. Industrial wastes are characterized by process-added chemicals that obscure the nature of the original raw water. In contrast, membrane concentrate has very few added chemicals and reflects the nature of the raw water. Those species rejected by the membrane are more concentrated than in the raw water. Membrane concentrate does not produce any additional pollutant material - it merely redistributes that present in the raw water. Membrane concentrate can in almost all cases be safely discharged or disposed of in some cost-effective and environmentally safe way. In some situations it is a resource that can be reused.

The industrial classification of membrane concentrate is just one of the unusual aspects of regulation of membrane concentrate that plays a role in calling attention to membrane drinking water plants.


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