Hardcover
-
PICK UP IN STORECheck Availability at Nearby Stores
Available within 2 business hours
Related collections and offers
Overview
Product Details
| ISBN-13: | 9781843390206 |
|---|---|
| Publisher: | IWA Publishing |
| Publication date: | 03/01/2006 |
| Series: | Integrated Environmental Technology Series |
| Pages: | 496 |
| Product dimensions: | 6.12(w) x 9.25(h) x 0.75(d) |
Read an Excerpt
CHAPTER 1
Introduction to pond treatment technology
Andy Shilton and Nick Walmsley
Pond treatment technology serves the wastewater treatment needs of agriculture, industry, cities and towns around the world and is one of the most common treatment technologies in use today. Indeed, for thousands of communities with many millions of people, from developing countries to modern industrialised nations, the only thing standing between raw wastewater and a local waterway is often a pond treatment system.
1.1 THE POND ENVIRONMENT
The main advantage of these systems is their simplicity to build and operate. Although these systems are often termed 'low tech', the mechanisms involved in the way they treat and stabilise pollution are as numerous and involved as those in conventional 'concrete and steel' technologies.
Thirumurthi (1991, pg. 231) noted, "the biology and biochemistry involved are the most complex of all the engineered biodegradation systems known to man."
To a large degree, the success of these systems can be attributed to the diverse environment that is established within the pond. Chapter 2 explains the microbiology and Chapter 3, the physical and chemical environment of the pond system.
Pond systems incorporate all aspects of conventional treatment including settlement of solids and BOD removal (see Chapter 4), disinfection (see Chapter 6), as well as offering some capability in terms of removal of nutrients and heavy metals (see Chapters 5 and 7).
1.2 THE 'STANDARD' POND SYSTEM
As pond technology has developed over the decades numerous names, for example sewage lagoons or oxidation ponds, have been used to describe the same thing. Thankfully in the last decade the work of various leading researchers, for example the design manual produced by Mara and Pearson (1998), has brought clarity to this confusion. Today there are reasonably well-established terminology and design procedures for what might be called the 'standard pond system'.
Figure 1.1 illustrates two variations of the common 'standard pond systems'. In the first of these the wastewater enters a facultative pond and then enters a series of maturation ponds. Because there is no prior treatment before the facultative pond (with the exception of screening and in some cases, grit removal) the term primary facultative pond is used. In the second illustration the pond system firstly, incorporates an anaerobic pond. The inclusion of an anaerobic pond can substantially decrease the size of the following ponds because, in this case, the wastewater is pre-treated by the anaerobic pond and the term secondary facultative pond is used. At the end of both these systems is a series of maturation ponds.
The main function of the maturation ponds is to provide for pathogen removal. In Figure 1.1 three maturation ponds are shown but in reality the number required is determined by design (see Chapters 8 and 9).
1.2.1 Anaerobic ponds
Designed to receive high organic loading, their treatment function is to undertake bulk removal of the organic load. They are normally absent of dissolved oxygen and contain no significant algal population. They are particularly effective in warmer climates but even in cold conditions they provide at least primary settling. With relatively short retention times of just a few days they can reduce the organic load by 40 to 70%. This significantly reduces the size requirements of subsequent ponds resulting in substantial land and cost savings. Many practical applications have shown that odour is not a problem if the recommended design loadings and sulphate concentrations are not exceeded.
1.2.2 Facultative ponds
Undoubtedly this is the most common type of pond in use throughout the world. The term facultative refers to the fact that these ponds operate with both aerobic and anaerobic zones. The lower layer functions with similar characteristics to an anaerobic pond. It consists of an anaerobic sludge layer overlaid with an anoxic zone in the water column. At higher levels in the water column the water becomes oxygenated due to the presence of high concentrations of oxygen producing algae. As will be discussed repeatedly throughout this book there is a classic relationship between the bacteria (an animal) and the algae (a plant). The algae produces oxygen which is then utilised by bacteria in the water column as they oxidise organic waste for energy and in turn produce carbon dioxide (and release nutrients from the waste material) which is used by the algae. In contrast to anaerobic ponds facultative ponds are relatively shallow (typically 1.5 metres) with retention times measured in weeks. Because these ponds depend on algae, which are 'driven' by sunlight, they are designed on an area basis as opposed to anaerobic ponds that are designed on a volume basis.
1.2.3 Maturation ponds
Maturation ponds typically follow facultative ponds in series. They have also been used for 'polishing' following conventional treatment. Their primary function is to remove pathogens, but they can also achieve significant nutrient removal (Mara et al., 1992). Although similar in appearance to facultative ponds, they have a low organic loading and as a result are well oxygenated. Typically, a series of smaller maturation ponds are used rather than a single large pond in order to ensure good hydraulic efficiency, which is particularly important when good pathogen removal is being sought.
1.3 POND DESIGN AND OPERATION
Numerous design equations have been proposed for ponds creating a large degree of confusion. Chapter 8 of this book reviews the various design methodologies that have been developed and in Chapter 9 a recommended design method is clearly outlined that will yield the sizing required for a standard pond system.
In addition to calculating the required pond size, the designer should also be aware of how the pond hydraulics (fluid flowpaths) are affected by design of inlets, outlets, baffles, wind and so forth and this is covered in Chapter 10.
In Chapter 11 the application and design of a range of techniques for further upgrading pond effluent quality, such as sand filters, rock filters, dissolved air floatation and so forth, are reviewed.
A well-designed pond system can still perform poorly if not operated effectively. Indeed, many of the problems encountered with pond systems simply result from operational issues such as the lack of regular sludge removal. Pond operation and maintenance is reviewed in Chapter 12.
1.4 OTHER POND TYPES AND SPECIAL APPLICATIONS
1.4.1 Fermentation/digestion pits
A recent innovation has been the concept of fermentation pits, as discussed by Oswald et al., (1994). Built within a facultative pond, this is a semi-enclosed pit operating under anaerobic conditions like a low-rate digester. The pit receives the raw influent and has a retention time of around one day. This design is reported to remove solids and organic waste more effectively than conventional anaerobic ponds. Because the oxygenated facultative pond overlies this anaerobic pit it is noted that these systems have less potential for odour release. The term 'advanced facultative ponds' is commonly used to describe this integrated pond/pit system. Further information on this technique can be found in Chapters 13 and 14.
1.4.2 Hi-rate algal ponds
Originally developed by Oswald at the University of California in the sixties (Shelef and Azov, 1987), these systems are shallower than a facultative pond (0.2 to 0.8 metres) and operate at shorter hydraulic retention times of around a week or less. A paddlewheel is incorporated to drive the water around a 'race-track' shaped pond. The oxygen production is reported to be significantly higher than typical facultative pond designs. The algae produced in these systems are also reported to have good settling properties (Green et al., 1996). Further information on this technique can be found in Chapter 13.
1.4.3 Advanced pond systems
There is increasing interest in the use of an integrated pond system which integrates an advanced facultative pond (with a built in fermentation pit) followed by a high rate algal pond (with recycle back to the facultative pond) followed by a series of maturation ponds. While still relatively limited in terms of the number of installations compared to the more standard pond systems previously detailed in Section 1.2, this system is one of the most popular areas of current research in the pond technology area. These integrated systems are reviewed in Chapter 13.
1.4.4 The PETRO process
The term PETRO stands for 'Pond Enhanced Treatment and Operation'. The PETRO concept basically involves using a waste stabilisation pond as a first stage to tackle the bulk of the organic load and then using a second stage process, such as a trickling filter (horizontal and vertical) or an activated sludge system for 'polishing' to improve the final effluent for removal of solids in nutrients. This technique has been particularly useful for upgrading overloaded trickling filter and activated sludge treatment systems. Refer to Chapter 14 for full details on ponds integrated with trickling filters and activated sludge processes and the PETRO process development.
1.4.5 Integrated ponds and wetland systems
Like ponds, wetland wastewater treatment systems are another type of 'natural' treatment technology. Wetland treatment technology developed after it was found that natural wetlands receiving wastewater discharges were actually able to provide significant treatment. Today artificial wetlands are constructed either as a 'surface flow system' (like a planted pond) or as a subsurface flow system (essentially a planted filter operated with either horizontal or vertical flowpaths). While not as widespread in application as pond systems (approximately 1/10) wetlands have a high deal of public appeal, in part due to the bird life they attract, and are rapidly growing in number. Because ponds and wetlands have the similar advantages of offering simple operation they are often used together to provide an integrated wastewater treatment solution. The application of wetland treatment systems is discussed in Chapter 15.
1.4.6 Aquaculture ponds
Throughout Africa and Asia it is not uncommon to add a fish or 'aquaculture' pond to the end of pond wastewater treatment system. The basic idea is that the fish will graze the algae reducing solids and subsequent harvesting of the fish then provides a source of protein and a method of recovering nutrients. Chapter 16 discusses the integration of aquaculture with pond treatment technology.
1.4.7 Storage ponds/reservoirs
There can be advantages in storing effluent within a pond as opposed to allowing to it continuously discharge. For example, effluent may be stored during winter periods when treatment is less effective due to colder temperatures. Other applications include avoiding discharge to a sensitive waterway such as a small stream at times when the stream flow is too low or during periods of algal blooms in the ponds. Apart from storing pond effluent for environmental reasons, storage is also used when the nutrient rich effluent is valued as a resource for irrigation during dry periods. Because these ponds are deep, to provide adequate storage volume, they are often referred to as 'reservoirs'. Chapter 11, which details an operation known as controlled discharge, and Chapter 18, which explores the use of ponds in cold climates, both discuss this technique. Chapter 17, however, is specifically focused on the design and application of storage reservoirs.
1.4.8 Cold climate ponds
Ponds are strongly influenced by climatic conditions because they are large water bodies that are exposed to the environment. This applies in a number of places. Because higher temperatures improve most treatment mechanisms the application of ponds are very effective in tropic and temperate regions. However, because of the advantages that ponds offer, particularly in terms of cost in regions where land is relatively inexpensive, they have still been widely applied in cold climates even when freezing conditions exist. A large amount of experience has been built up for the design and operation of ponds in cold climates and this is reviewed in Chapter 18.
1.4.9 Agricultural wastewater ponds
Perhaps the most common application of pond treatment technology is the numerous small pond systems that treat wastewater from dairy milking sheds, piggeries and other farming activities. As for domestic wastewater treatment, these applications typically utilise the standard anaerobic/facultative/maturation type pond system. However, as is discussed in Chapter 19, agricultural waste is very different to domestic wastewater requiring special consideration and design.
1.4.10 Stormwater ponds
There is increasing awareness that stormwater flushed off an urbanised catchment is not simply clean rainwater but contains a range of contaminants such as solids and heavy metals. Ponds, often supplemented with wetland plantings, are increasingly being installed to treat stormwater. Stormwater ponds have short retention times, typically of just a few days. They provide buffer storage to reduce runoff peaks, and also provide enhancement of stormwater quality by various treatment processes such as settlement of solids. As part of their design strong emphasis is also placed on the creation of recreational and habitat amenities. Chapter 20 details the function and design of stormwater ponds.
1.5 WATER QUALITY AND REGULATORY ISSUES
While algae are of critical importance to the effectiveness of pond systems, its growth in the pond and subsequent discharge does contribute to elevated unfiltered BOD and solids concentrations in the final effluent if not removed prior to discharge (see Chapter 11 for algae removal techniques). Where regulators implement strict effluent standards for BOD and/or solids this can create an issue. However, a number of researchers have questioned the appropriateness of applying strict standards to pond effluent containing algae given that the algae is a plant rather than a sewage solid. In many areas regulators recognise this difference and set standards to allow for the algae in the effluent. Chapter 9 discusses this issue further.
In addition to BOD and suspended solids, pathogens are also often monitored. Pond systems can be very effective at disinfection – see Chapter 6. Discharge standards for nutrients have been less common, but this is changing and is certainly an important issue for future consideration.
Chapter 9 provides a process design methodology for sizing ponds in relation to achieving water quality standards.
1.6 EVALUATION OF THE TECHNOLOGIES
Perhaps the two most critical factors that influence selection of any particular wastewater treatment option are performance and cost.
The level of performance of a pond system is obviously flexible depending on the system design. A simple anaerobic pond in a cold climate can give primary level treatment whereas more sophisticated pond systems can yield high removal of organics and effective disinfection. There are also possibilities of adding on additional units such as filters to further enhance the effluent quality. In Chapter 11 a review is presented that compares ponds systems with other treatment technologies and shows how a pond system can produce effluent qualities as good as or better than other conventional treatment options such as activated sludge.
The cost advantages of ponds were analysed by Arthur (1983), in an often-referenced World Bank Technical Paper, and shown to be most cost effective provided that land costs were not high. This was reconfirmed in more recent times by UNEP (1999) as summarised in Table 1.1. It is important to note that in addition to the BOD and nitrogen removal cited in this table, ponds are also capable of providing a high level of pathogen removal as part of their standard design.
(Continues…)
Excerpted from "Pond Treatment Technology"
by .
Copyright © 2005 IWA Publishing.
Excerpted by permission of IWA Publishing.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Table of Contents
Foreword, xii,
Dedication, xiii,
Contributors, xiv,
1 Introduction to pond treatment technology Andy Shilton and Nick Walmsley, 1,
2 Microbiology of waste stabilisation ponds Howard Pearson, 14,
3 Physical and chemical environments Charlotte Paterson and Tom Curtis, 49,
4 Solids and organics Nick Walmsley and Andy Shilton, 66,
5 Nutrients Rupert Craggs, 77,
6 Pond disinfection Rob Davies-Colley, 100,
7 Heavy metal removal Rupert Craggs, 137,
8 Pond process design – an historical review Andy Shilton and Duncan Mara, 145,
9 Pond process design – a practical guide Duncan Mara, 168,
10 Hydraulic design Andy Shilton and David Sweeney, 188,
11 Solids removal and other upgrading techniques E. Joe Middlebrooks, V. Dean Adams, Stuart Bilby and Andy Shilton, 218,
12 Operation, maintenance and monitoring Barry Lloyd, 250,
13 Advanced integrated wastewater ponds Rupert Craggs, 282,
14 Pond(s) integrated with trickling filter and activated sludge processes Oleg Shipin and Pieter Meiring, 311,
15 Integrated pond/wetland systems Chongrak Polprasert, Thammarat Koottatep and Chris Tanner, 328,
16 Integrated pond/aquaculture systems Chongrak Polprasert and Thammarat Koottatep, 346,
17 Wastewater reservoirs Marcelo Juanicó, 357,
18 Cold and continental climate ponds Sonia Heaven and Charles Banks, 381,
19 Ponds for livestock wastes James Sukias and Chris Tanner, 408,
20 Stormwater management ponds Jiri Marsalek, Ben Urbonas and Ian Lawrence, 433,
Index, 461,