Our discussions on water treatment began by making the analogy of a water treatment facility with any other manufacturing operation. The similarity between a water treatment facility and any manufacturing operation, whether it be a rubber producing plant or an auto-making facility or an iron and steel plant, are the reliance upon combinations of unit processes and unit operations that work in harmony to produce a high quality product. But that is where the similarity ends. A normal manufacturing operation aims not only to produce a high quality product, but efficient businesses strive to do so by eliminating or minimizing their wasteful by-products - simply because those by-products have little to no market value and add cost to production. If our cost of production is higher, then profit margins are lower. That in fact is the basis for pollution prevention and waste minimization practices of modern-day industry.
A water treatment facility differs in this regard because the primary objective is to produce high quality water by removing or destroying as much of the contaminants as possible. We cannot produce high quality water without generating the wasteful by-product, sludge, very often in large quantities. Water treatment plants are simply pollution control technologies, whether they are applied to industrial applications or municipal. That does not mean that pollution prevention practices are not appropriate for water treatment plants - they most certainly are and can minimize solid waste generation. But understand that we cannot eliminate the wasteful byproduct of sludge as one might try and do if we had an manufacturing facility and we identified another technology to make our product arid eliminate a wastestream generated by the older technology.
Sludge or solid waste is unavoidably produced in the treatment of water containing suspended solids. There are, however different technologies that we can select among that will indeed concentrate these solids, and thereby reduce the volumes that we ultimately must dispose of. In addition, some sludge can be stabilized and treated, which can impart a low, but none-the-less marketable value to this waste. These technologies and practices do indeed constitute pollution prevention and waste minimization programs within water treatment plant operations, and they can have a very significant and positive impact on the overall costs of the operation. This brings us to a collection of technologies that focus on: (1) sludge concentration, (2) sludge stabilization, (3) sludge handling and disposal. Some technologies fall into the category of pollution prevention, while others are within the normal arena of solid waste management and disposal. Note that pollution prevention or P2 technologies, as in other industry sectors, are not necessarily the preferred choices. Specific technology selection quite often depends on localized conditions. By this, we mean the properties of the sludge, the volumes handled, and the comparative costs between technologies and or practices. In a very general sense, pollution prevention technologies are only appropriate when they are financially attractive for an operation. Like any other engineering project, the investment into a technology that falls within the pollution prevention arena must have financial attractiveness. An alternative way of stating this is that there are indeed situations where more conventional methods resulting in large volumes of sludge are more cost effective than a leading-edge technology that minimizes or reduces sludge volumes. The financial attractiveness of an investment needs to be assessed on a case by case basis.
This final chapter focuses on sludge processing and post-processing technologies. Where appropriate, we will point out which technologies may be considered P2. Recommended resources are given at the end of this chapter that will assist you in evaluating the relative investments required, as well as in obtaining more detailed technical information. There is also a section on Questions for Thinking and Discussing, which will help you to generate ideas and approaches to selecting cost-effective methods. Remember to refer to the Glossary at the end of the book if you run across any terms that are unfamiliar to you.
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