Modern Techniques in Water and Wastewater Treatment

Modern Techniques in Water and Wastewater Treatment

This book is the outcome of the CSIRO/UNIDO workshop in wastewater treatment. The papers presented at the workshop and published in this book provide an insight into the characteristics and applicability of the various methods used to treat water and wastewater as well as examples of both the theory and practice of these technologies.

The authors include research scientists, technical consultants and industry practitioners who provide a wide range of views.

  1. Page iii
  2. Page vii
    1. Page 7

      Coagulation and flocculation processes are widely used in water and wastewater treatment to remove undesirable particulate colloidal and suspended impurities.

      The size and surface characteristics of a particulate impurity are both important parameters affecting its separation from solution. The efficiency of the physico-chemical processes for removing such impurity increases with increasing size and decreasing surface charge. Coagulation and flocculation processes are used to reduce the surface charge and to promote the agglomeration of the colloidal or suspended impurity to form large, settlable, floatable and/or filterable agglomerate called floes.

      The chemical-physical and engineering aspects of the coagulation-flocculation processes are discussed in this paper.

    2. Page 15

      Australia does not experience the intensity of water-borne disease of other countries, however, it is still essential that our water supplies, which are accepted completely by the public, are safe, and this means that they must be properly disinfected. Chlorination only of raw water is probably often inadequate as the water may not be clear, or if clear it may not be free of pathogenic cysts. Cost of water treatment is small, around 0.25% of a household’s current budget. Benefits of water treatment include the removal of clay which causes turbidity and harbours virus and bacteria, of the organic molecules which colour the water and hinder disinfection, and of algae, iron and manganese. Water corrosivity can also be corrected with resulting extension in the life of water mains and customers’ plumbing.

      Modern Australian treatment processes are well understood and cost effective. Dissolved Air Flotation/Filtration (DAFF) is a particularly cost-competitive and effective process, especially for raw waters containing high colour or algae.

    3. Page 19

      The plant scale ‘Chemically Assisted Sedimentation’ (CAS) evaluation trial at Cronulla sewage treatment plant undertaken by the Technology Development Unit of the then Water Board, Sydney, was a direct consequence of recommendations contained in a 1989 report prepared by Camp, Dresser & McKee for the Minister for the Environment (NSW). Using ferric chloride as the coagulant and a commercial anionic polymer as the floccuiant, the performance characteristics of the CAS on the supplied influent was determined on both a continuous and a diurnal basis. Three ferric chloride doses (23, 34 and 45 mg L−1 as FeCl3) were trialled in sewage while the polymer dose was kept constant.

      It was found that CAS was effective in markedly improving effluent quality and that above a dose of 23 mg L−1 ferric chloride there was no significant further improvement in effluent quality. The removal efficiency at a dose of 23 mg L−1 was 80% for total suspended solids (TSS), 83% for oil and grease (O&G) and 65% for biochemical oxygen demand — 5 day (BOD5). This represents an overall improvement over nil dose of 11% for TSS, 26% for O&G and 31% for BOD5.

      As there are diurnal variations in the TSS concentrations of both influent and effluent, it may be necessary when operating full-scale CAS plants to determine an overall chemical dose level and to optimise this dose in relation to TSS concentrations to reduce overall costs.

    4. Page 25

      SIROFLOC™ technology, based on the use of magnetic particles for water and wastewater treatment, was discovered by CSIRO in 1977. The process was first used to produce high quality drinking water and it has now been adapted to the purification of sewage.

      The SIROFLOC processes are very fast physico-chemical purification processes in which particles of magnetite (Fe3O4), a commonly mined mineral, are used as a solid, reusable coagulant-adsorbent and weighting agent. Magnetite is used alone or in conjunction with a suitable secondary reagent such as polyelectrolyte or alum to remove particulate and some dissolved impurities from water or wastewater. When magnetically flocculated, the impurity laden particles are separated rapidly from the treated water. The loaded magnetite is then reactivated with acid or alkali, rinsed and reused. When magnetite is used with alum, the alum can also be recovered and recycled. The impurities are concentrated into a small volume for disposal.

      A number of commercial plants have been built in Australia and the UK. China, Malaysia and Germany are also showing a strong interest in this technology. The process is protected by a number of international patents; Davy John Brown Pty Ltd has the licence to install the treatment plants worldwide and can grant sub-licences.

    5. Page 35

      This paper describes the lime-assisted primary treatment process and its performance in the removal of suspended solids, phosphorus and heavy metals from non industrial domestic sewage. This process is seen as a viable means of sewage treatment in areas where there is domestic and industrial waste with heavy metals contamination and where there is a need for the staged introduction of full secondary or tertiary effluent treatment, but where the funding in the short term precludes the construction of all processes needed to achieve this level of treatment.

      The paper draws on experience which has been gained by the Australian Capital Territory Electricity & Water Authority (ACTEW) in the operation of lime assisted primary treatment at the Lower Molonglo Water Quality Control Centre (LMWQCC), a full tertiary treatment plant. ACTEW’s facilities at Lower Molonglo are recognised as a benchmark in wastewater treatment, particularly in the removal of phosphorus.

    6. Page 41

      Pressure-driven membrane processes have been increasingly applied to water and wastewater treatment since the development of reverse osmosis as an economically viable desalination process in 1960. A wide range of membranes is now available, with many multi-ML d−1 installations operating around the world.

      Depending on the nature of the contamination in the water supply and the intended use of the product water, microfiltration (MF), ultrafiltration (UF), nanofiltration(NF) and reverse osmosis (RO) can be used. The general principles of these processes are described in this overview, some of their advantages and disadvantages are outlined, and typical product water costs estimated.

      The next two papers in this volume discuss the MF and RO processes in detail.

    7. Page 45

      The purpose of this paper is to provide an overview of Continuous Microfiltration (CMF)1 in water and wastewater treatment. There are now over 350 CMF plants installed on applications ranging from high purity water to primary treated sewage in 14 countries around the world.

      The CMF system employs a polypropylene microfiltration membrane capable of removing bacteria and viruses and a unique air backwash which prevents membrane fouling and bacterial growthrough. This allows the filter to be used on a wide range of feedstreams for particulate removal with the membrane element lasting up to five years.

      This paper will explain how the technology works, cover performance and examples in water and wastewater treatment, outline typical equipment configurations and compare capital and operating costs.

    8. Page 53

      Commercialisation of reverse osmosis (RO) occurred in the early 1970s. It is now an accepted technology world-wide for desalination of brackish water and seawater, and the concentration of or treatment for recovery of industrial wastewater. In Australia, there are over one thousand RO plant installations. The majority are used for desalinating brackish waters. There are a few seawater desalination plants and a limited number of industrial wastewater treatment facilities.

      The first Australian RO plant was installed in 1973. Most of the existing Australian RO plants have been designed and constructed by Australian water treatment engineering contractors. There is now considerable wealth of knowledge and experience in this country on the requirements for pre-treatment to suit Australian waters, operational (process control), maintenance aspects and membrane selection. The membranes utilised in the Australian plants are predominantly of spiral wound design and of US origin.

      The use of RO desalination in Australia is uniquely different from that of the rest of the world and is dominated by applications for remote regions where water suitable for domestic consumption is at a premium.

      The current experience in Australia with RO technology is addressed in this paper by way of case studies of existing installations. The opportunity in the future for innovative application of RO technology is highlighted by reference to research projects being undertaken by the Cooperative Research Centre (CRC) for Waste Management and Pollution Control Limited. The CRC is an Australian research centre of excellence and the membrane related research projects currently underway represent the CRC’s largest research programme, with planned expenditure of around $6 million. This investment is likely to return a rich harvest given the large and rapidly growing market for membranes for treatment of waste and wastewater to solve significant environmental problems.

    9. Page 61

      Ionic impurities such as heavy metal cations or Chromate ions can be removed from wastewater by ion exchange. Residual metal concentrations are typically less than 1 mg L−1. Exhausted ion exchanger is regenerated, usually with acid, and reused. Regeneration yields a concentrated solution of a metal salt, which in favourable cases can be recycled. Alternatively metal salts can be converted electrolytically to the free metal Treated water can also be recycled. Ion exchange equilibria can be manipulated to allow a single valuable species to be separated from a mixed wastewater. The most common type of ion exchange equipment uses a fixed bed of resin beads. Novel moving-bed systems based on magnetic resins use small quantities of resin and are able to treat wastewaters containing suspended solids.

    10. Page 65

      The role of soluble polymers in water purification is discussed, with an emphasis on interactions at the molecular level. Some knowledge of the impurities present in natural waters is essential to gain a better understanding of how to clean up low grade resources in an efficient and economic manner.

      Processes where polymers are used successfully include conventional coagulation and flocculation which are normally followed by sedimentation and filtration, analogous processes where a weighting agent or the like is employed, direct and contact filtration in the absence of a settling stage, dissolved air flotation, induced air or foam flotation, enhanced primary treatment of sewage and sludge thickening.

      There are several benefits arising from polymer use: a dramatic increase in the throughput of a plant, a lowered usage of other chemicals, significantly decreased sludge volumes and a widening of the range of water resources which can be utilised. These must be balanced against higher additive costs.

    11. Page 75

      Water and wastewater disinfection is carried out to protect human health by minimising the transmission of water-borne disease-causing micro-organisms. Emerging concerns include cyst-forming organisms such as Giardia lamblia and Cryptosporidium.

      Chlorination is the oldest, least expensive and most commonly used disinfection agent, but concerns about chlorinated disinfection by-products have called its use into question, especially in some countries in North America and Western Europe. Extensive research in the past 20 years has led to improved processes to maximise disinfection efficiency whilst minimising by-product formation and overall health risks.

      Alternatives to chlorine are available and the advantages and disadvantages of some of these are enumerated. Chemical disinfectants include chloramine, bromine, chlorine dioxide, ozone, iodine and silver ions. Some must be generated in situ, some may leave no residual, some may liberate undesired by-products and others are prohibitively expensive.

      Physical processes have also been used. These include UV radiation, microfiltration, heat, ultrasound and γ-radiation, although only the first is in common use for disinfection purposes.

      Because of the large number of organisms potentially present, indicator organisms are traditionally used to monitor the efficiency of the process. The properties of suitable indicator organisms and the selection of process conditions to ensure adequate disinfection, in particular the C*t concept, are discussed.

      Post-disinfection, maintenance of a disinfectant residual in the distribution system is essential to avoid regrowth of surviving organisms. Whether disinfection of secondary-treated wastewater is justified is also addressed.

    12. Page 81

      Ultraviolet radiation (UV) can be used for the disinfection of water and wastewater because of its ability to interfere with the replication of micro-organisms. When applied within the known limitations, good results can be achieved. The required radiation dose is dependent on the microbiological load — the types of organisms present and their number. For most drinking water applications, a real dose of 30 mW.s cm−2 after losses in the system is considered acceptable, but higher doses may be required for wastewater effluent disinfection. The treatment system must be designed to ensure that the whole water flow receives the required dose under a worst case scenario. Water quality parameters such as UV absorb ance and turbidity diminish the applied dose and hence influence the flow rate at which the water can be treated. Acceptance tests must include an allowance for deterioration of lamp performance with time.

      This paper presents an overview of lamp and contactor technology and discusses the advantages and disadvantages of the process. Some examples of applications of the technology in Australia are also provided.

    1. Page 91

      Aerobic biological treatment systems have been the predominant form of secondary treatment for municipal wastewater and many industrial wastewaters for the past half century. Both fixed film and free loating (activated sludge) biological systems, combined with a solids separation process can provide high quality effluents. The activated sludge systems are particularly suitable for the removal of nitrogen and phosphorus, but require appropriate configuration of the bioreactor.

    2. Page 99

      A major and growing need exists for cost-effective nutrient removal processes. The largely Australian developed cyclic processes could be competitive with better established continuous processes, particularly with medium and small scale plants. Australia has the know-how to become a major supplier of all-biological nutrient removal technology.

    3. Page 103

      Development of the Melbourne Solution was stimulated by the potential for algae, zooplankton and seaweed to be used as renewable sources of food in aquaculture, and the need to provide water quality guarantees for the future development of fishing industries. It has long been recognised that correctly designed and managed sewerage systems, based on stabilisation ponds, can deliver substantial quantities of aquatic food materials as well as a low cost system of managing water quality on a large scale. The paper describes the approach taken at the large Werribee sewage treatment ‘farm’ and prospects for the future.

    4. Page 107

      Barwon Water is constructing a new 70 ML d1 secondary sewage treatment plant at Black Rock, Victoria, to treat domestic and industrial wastewater from the City of Geelong, a major regional centre with a population of close to 200000.

      The process to be employed at the new plant is the intermittently decanted extended aeration (IDEA) process. This process was selected following extensive pilot plant investigations of this and other commonly used sewage treatment processes.

      The paper describes the pilot plant investigations and presents the results of the experimental work. The IDEA system was eventualy selected for the A$42 million upgrade based on comparison of the following factors:

      • pollutant removal efficiency;

      • ability to meet EPA requirements;

      • ability to cope with shock organic and hydraulic loadings;

      • reliability, flexibility and robustness;

      • required routine operator intervention;

      • potential for odour production;

      • capital and operating costs.

      Construction of the plant commenced in March 1994 and is due to be completed by December 1995.

    5. Page 115

      In 1988, a $4.1 million augmentation of the Ballarat South Wastewater Treatment Plant was commissioned. Its objectives were to provide increased treatment capacity to the year 2010 and to meet new Environment Protection Authority (EPA) licence requirements of a 10 mg L−1 ammonia concentration limit and a 2 mg L−1 total phosphorus concentration objective.

      This paper details performance of this high rate plant before and after augmentation of the plant with a settled sewage flow balancing tank and a third aeration tank. These additions cost $1.0 million.

      The licence objective on phosphorus is still not being met, although optimisation of process control and operating conditions is still proceeding, following commissioning of the third aeration tank late in 1993.

    6. Page 121

      The Bendigo Biological Nutrient Removal Plant was designed to consistently achieve a high degree of both nitrogen and phosphorus removal, operating in the Modified UCT process. It also represented the largest biological nutrient removal plant constructed in Australia.

      The city of Bendigo is situated 150 km north of Melbourne. The treatment plant is designed for a contributing population of 120000 equivalent persons. The treatment plant is required to meet effluent limits of 10 mg L−1 biochemical oxygen demand, 15 mg L−1 suspended solids, 2 mg L−1 ammonia nitrogen and 10 mg L−1 total nitrogen.

      The limit for effluent phosphorus has not been rigidly set by the Victorian Environment Protection Authority, requiring only that the plant maximise biological phosphorus removal. Pilot plant trials and fundamental design equations indicated that a phosphorus level of 2 mg L−1 could be achieved and this was subsequently adopted as the treatment objective.

      Commissioning commenced in May 1991. The onset of nitrification was slow due to the cold sewage temperatures (14°C) experienced at the time of commissioning. Since then the effluent ammonia and total nitrogen levels have been extremely stable. The plant is achieving effluent ammonia nitrogen levels less than 0.2 mg L−1 and total nitrogen levels consistently below 10 mg L−1.

      Phosphorus removal commenced with normal metabolic uptake (2–3 mg L−1) for the first six weeks after start-up. The onset of biological phosphorus removal began following the sixth week and the phosphorus treatment objective was achieved within sixteen weeks after start-up. Subsequent plant operational problems and changes resulted in loss of biological phosphorus removal, but recovery was attained within ten weeks of correction to the plant operation.

      The commissioning of the Bendigo Plant has proven the suitability of biological phosphorus and nitrogen removal technology under Australian conditions when treating predominantly domestic sewage.

    7. Page 127

      This paper gives an overview of Biological Aerated Filters (BAF) treatment system, which is an attached growth process. There are a number of variations to Biological Aerated Filters and the system that will be explained in some detail is that developed by Thames Water: the SAFe process.

      The advantages and disadvantages of BAF over other conventional aerobic treatment systems will be discussed.

      Operational data from Silchester Waste Treatment Plant in the UK will be included and discussed.

    8. Page 133

      During the past 25 years a variety of high-rate anaerobic reactors have been developed which have enabled anaerobic digestion to become a viable treatment option for large volume industrial wastewaters. A number of reactor configurations, e.g. anaerobic filter, upflow anaerobic sludge blanket and anaerobic fluidised bed, are currently used at full scale for the treatment of wastewaters from the food processing, brewing, distilling, paper and chemical industries. This article provides a brief overview of the microbiology, reactor configuration, applicability, monitoring and control of high-rate anaerobic digestion for wastewater treatment.

    9. Page 141

      The Western Treatment Plant (formerly the Werribee Treatment Complex) is a major lagoon and land treatment works situated 35 km to the west of Melbourne. It is also a large beef-cattle and sheep station and a wildlife refuge of international significance. To ensure that sewage treatment operations at the Western Treatment Plant are developed in a sustainable fashion, a major lagoon redevelopment program is underway to control odour and improve performance, with covered anaerobic ponds and aerated-facultative ponds a prominent part of the new generation lagoons.

      Ongoing research by Melbourne Water aims to optimise methane yields for electrical energy production and nutrient removal, and minimise aerator usage. Other lagoon research activities include the use of biofilms to enhance nitrogen removal and, in conjunction with Zootech Research Pty. Ltd., the large scale production and harvesting of zooplankton as a means of nutrient and algae removal. Zootech is independently developing aquacultural fishfoods from the harvested zooplankton and is embarking on hatchery operations and investigations into offshore seaweed production for a range of processed animal and human food products and chemicals.

      This paper describes, in particular, the historical development of lagoons which feature covered anaerobic reactors and aerated ponds, and discusses the various design and operational problems that have been encountered. The paper also outlines current and planned research on the lagoon process, and future directions for the Western Treatment Plant.

    10. Page 149

      This paper summarises the overall issues associated with the development of lagoon systems. The principal issues addressed are odour, effluent requirements, aeration and sludge management.

      Each issue is discussed to illustrate the governing factors and proposed solutions to overcome shortfalls against objectives for minimised environmental and community impact.

      The overall advantages and disadvantages are highlighted to allow informed decision making regarding the installation of lagoons as a treatment process to be considered further for particular applications.

    11. Page 155

      Anaerobic digestion as a treatment process for wastewater has been in use for many years, but was often regarded as a slow process and therefore occupying a large space. Develpoments in the last 20 years include a more complete understanding of the biochemistry involved, and the discovery of the pelietization of the sludge when the process is operated in the upflow sludge blanket mode. This led to the naming of the process the Upflow Anaerobic Sludge Blanket (UASB) treatment system. The main advantage of this system is that the higher density of micro-organisms in the reactor allow the treatment to proceed at much higher rates, with a proportional decrease in the size and cost of the treatment plant. Such treatment plants are now widely used in the food industry and for other high strength organic wastes.

    1. Page 163

      Sludges generated during water treatment have become an environmental problem as their volumes increase and traditional disposal options such as ocean disposal are being disallowed. Landfill is currently one of the most common disposal options but requires sludges that are dewatered up to ‘spadable’ consistency, typically between 17–20 wt% solids. Mechanical dewatering of water sludges is often difficult and requires careful conditioning with polymers. Significant scope also exists for the development of innovative dewatering methods. Electro-osmotic aided pressure filtration of alum sludges at laboratory scale resulted in 30 wt% cake solid contents compared with about 12 wt% obtained with pressure alone. Efficient sludge dewatering opens prospects for economically viable reuse options. Thus, a process to recover aluminium from dewatered alum sludges by alkaline leaching has been designed. Addition of the recovered aluminium to wastewater was effective to reduce the phosphorus content from 9 to below 1 mg L−1.

    2. Page 171

      Disposal of sludges has presented many problems to the sewage industry and there are various health and environmental constraints to their use and disposal. Recently there has been a change towards reuse or recycle solutions and there are a number of such facilities operating in Australia. There are many considerations in choosing a path for sludge disposal. In this paper, a brief outline of Australian sludge management practices, followed by examples of current operations, is developed into a description and comparison of today’s options.

    3. Page 177

      The development and evaluation of options for biosolids management has involved the collection and analysis of information related to the quantity and quality of biosolids, and their market, transportation and biosolids processing assessments. As well as a broad technical and environmental evaluation of the available options, a detailed Net Present Worth analysis of 37 options has been carried out. The analysis has been based on year 2021 projected sludge capture of 440 dry t d−1 (c.f. 194 dry t d−1 in 1994). Preferred products, transportation modes and markets have been determined.

      Management strategies aimed at achieving a particular objective can be developed that comprise a mix of biosolids management options. Cost of various management strategies are described. For Sydney, the production of digested dewatered cake with end uses primarily in agriculture and forestry (with a small proportion to landfill) will represent the lowest cost strategy. A more diverse beneficial use strategy will reduce market risk, but significantly increase costs.

    4. Page 183

      A multi-disciplinary team from CSIRO has developed a continuous on-line sewer monitoring system to measure a suite of basic physico-chemical parameters (temperature, pH, conductivity, turbidity and dissolved oxygen), which reflect the bulk properties of sewage. Specialised sensors are mounted in a flow manifold fed by a submersible macerating pump. The inherent scouring action of the flowing effluent was found to minimise fouling build-up, and the system has been proven to operate reliably in a broad range of effluents for several months with little attention.

      Most sewer discharges will affect at least one of the variables measured, so the system is able to detect a wide variety of discharge events, ranging from hot wash water to electroplating wastes. It can police discharges in industrial estates, monitor diurnal trends in domestic catchments, and can be used to optimise treatment plant performance. Field trials have been conducted in a wide range of sewage effluents, where it successfully detected illegal and unsuspected discharges. The system is compact and readily portable, and can be used both at fixed sites or as a mobile trade waste inspection unit. It is now available commercially as the Sewer Sentinel* and more than ten units have been sold. They have proved most reliable in monitoring a range of sewage and industrial effluents.

    5. Page 200