1 South African Sludge Management Guidelines Innovation and Impact Heidi G. Snyman * Water Research Commission, Private Bag X 03, Gezina, 0031, Gauteng, South Africa ( Abstract South Africa has completed the development of their new Wastewater Sludge Guideline Series. The new three tier sludge classification system includes microbiological limits, stability criteria and pollutant limits. These limits are based on international and local research results while factors such as legislation, technology and the sector s ability to absorb the guidelines were also taken into account. The guidelines are published in five volumes each dealing with a specific management option(s). These volumes deal with the selection of appropriate sludge management option(s) based on the characteristics and classification of the sludge and the requirements for the following management options: (1) agricultural use, (2) on-site and offsite disposal; (3) beneficial use of sludge and high loading rate use in agricultural practices; (4) thermal sludge management practices and, (5) for commercial products containing sludge. The different volumes for different management options simplify the understanding of the requirements and restrictions that pertain to a particular management option. The paper details the specific metal limits for each management option. The paper also highlights the results of an impact study which details the potential impact of the application of the guidelines in the society. Keywords Metal limits, sewage sludge, sludge guidelines, South Africa, wastewater sludge. INTRODUCTION This paper presents an overview of the wastewater sludge management approaches in a typical developing country (South Africa), it summarises the content of the newly developed South African Sludge Guideline Series and state the preliminary impact of applying these guidelines providing a valuable case study for other developing countries. The concept of sustainability was adopted as the ideal during the development of the 2nd edition of the Sludge Guidelines. Sustainable management options include options that do not harm the environment by either the use of a non-renewable resource or a build-up of substances in the environment to the extent that the assimilative capacity of the receiving environment has been exceeded. Unsustainable management options include disposal practices such as stockpiles, certain landfill and sacrificial land disposal practices. With current knowledge, there are three ways in which sludge management can contribute to sustainable development: (1) Utilising the calorific energy value of the sludge (example: generating heat); or (2) Utilising useful constituents such as carbon and nutrients (example: agricultural use); or (3) Extracting useful constituents from the sludge (example: extraction of phosphorus). Most agree that the second option i.e., utilising the useful constituents such as carbon and nutrients in the sludge, particularly in support of agricultural practices, is the most viable management option for South Africa. However, one also needs to be realistic and recognise that not all sludge generated in South Africa is suitable for agricultural use. It was therefore necessary to develop guidelines for other management options such as disposal and incineration and also provide opportunity for innovation. Each sludge management option was developed as a separate guideline volume. This simplifies the Guidelines for users, as each guideline focus on the management, technical and legislative aspects associated with a particular option. Each of the management options has different regulatory requirements and the sludge classification requirements for each option vary. At the same time it was important to understand whether the sector was ready and able to adopt the new guidelines. Developing countries often develop policies and guidelines for the sustainable management of the environment and waste comparable with those applied in developed countries. The implementation of these policies and guidelines are often seen as being costly and unpractical. This paper therefore also details the benefits (and shortcomings) of implementing sustainable
2 sludge management guidelines in a developing country. The aim of the impact study was to quantify the potential impact of the Sludge Guidelines on South African society by analysing current examples of wastewater sludge best practice that are aligned with the new Sludge Guidelines. WASTEWATER SLUDGE USE AND DISPOSAL PRACTICES IN SOUTH AFRICA The statistics regarding the use and disposal of wastewater sludge was presented by Snyman (2007). Half of the approximately 970 wastewater treatment plants in South Africa treat less than 500 m 3 /day (< 0.5 Ml/day) and a further 11% treat between 500 and 2000 m 3 /day. There is little information on the sludge handling practices of these small plants, although it is suspected that most of the sludge is accumulated on site. A survey of 72 wastewater treatment plants (Snyman et al., 2004) which focused mainly on the plants larger than 2000 m 3 /day revealed that majority of sludge that is used/disposed is anaerobically digested sludge (primary and humus sludge). Waste activated sludge accounts for 25% of the mass of sludge produced. Sludge is dewatered either in drying beds or mechanical belt filter presses or centrifuges. Where no dewatering technologies are employed, liquid sludge is often used for direct land application such as dedicated land disposal and instant lawn cultivation. Anaerobic digestion of primary and humus sludge is still employed to stabilise the majority of the sludge generated in South Africa. The majority does not treat the sludge further than the traditional anaerobic digestion and activated sludge extended aeration. Composting is used by both metropolitan city councils and plants in smaller town councils while pelletisation is only employed by large metropolitan areas (Snyman et al., 2004). Final disposal methods employed by the wastewater treatment plants surveyed in South Africa are still dominated by on-site disposal methods. This includes direct land application and stockpiling of the sludge on site. The beneficial use of sewage sludge is still limited. Stockpiling and disposal practices noticeably increased after the publication of the 1997 sludge guidelines (WRC, 1997) as these guidelines were perceived to be overly strict and unattainable. This was one of the reasons why an addendum was published in 2002 (WRC, 2002) and a dedicated research programme was initiated to develop sustainable appropriate guidelines. The South African wastewater treatment sector remains conservative in terms of the technological choices. Innovative technologies such as the electro-osmotic belt filter press (Snyman et al., 1999) and innovative commercial solutions are isolated or remain at the demonstration plant level. SLUDGE LEGISLATION IN SOUTH AFRICA The South African based Water Research Commission initiated a research programme to further develop the knowledge base for the management of sewage sludge in the South African context. Although the results of these research projects did not address all the unknown factors, it provided enough information to develop a new set of guidelines for the management of wastewater sludge in South Africa. The South African wastewater guidelines replaces all previous guidelines are now being implemented by the local authorities. The Department of Water Affairs stipulate in the authorisation of the treatment plant that the Guidelines should be adhered to and through this process the Guidelines become legally binding. The South African guidelines comprise of a set of 5 Volumes (Herselman et al., 2009; Herselman and Moodley, 2009; Herselman and Snyman, 2009a; Snyman and Herselman, 2006a; Snyman and Herselman, 2006b) and scientific support documents (Herselman, 2009a; Herselman, 2009b; Herselman and Snyman, 2009b; Snyman and Herselman 2006c) which detail the background literature that informed the guidelines as well as the scientific research methodology and findings, risk assessment and premise for the guideline. The major aspects of each of these volumes are discussed in the sections that follow. The limits set for the microbiological class and the stability class remains essentially the same throughout the 5
3 volumes (Snyman et al., 2006). However, the methodology and limits for the pollutant class differs depending on the most sensitive receptor and legal framework of that particular use. Specific discussions regarding the metal limits for each use are therefore presented. Volume 1: Selection of Management Options Volume 1 (Snyman and Herselman, 2006b) describes the initial comprehensive characterisation of the sludge. Based on the results of the characterisation, the sludge is classified according to the new classification system (Table 1). Limits and criteria for the microbiological class, stability class and pollutant class are detailed by Snyman and Herselman (2006bc). In Volume 1, limits are presented for 8 metals which are used for classification purposes and benchmark values are presented to highlight potential risks (Table 2). Table 1. The South African wastewater sludge classification system (Snyman and Herselman, 2006bc) Classification class Best quality Intermediate quality Worse quality Microbiological class A B C Stability class Pollutant class a b c Table 2. Metal limits to determine the pollutant class for the preliminary classification of wastewater sludge to assess possible management options (Snyman and Herselman, 2006bc). Aqua regia extractable metals (mg/kg) Pollutant class a b c Elements for As < >75 classification (risk Cd < > 85 based limits) Cr < > Cu < > Pb < > 840 Hg < > 55 Ni < > 420 Elements for benchmarking purposes to identify potential risks (20 th percentile for class a, between 20 th and 80 th percentile for class b and 80 th percentile values for class c) Zn < > Sb < >7 B < >72 Ba < >250 Be < >7 Co < >38 Mn < >1225 Mo < >12 Se < >15 Sr < >205 Tl < >0.14 V < >430 An appropriate management options can be selected based on the classification results. All sludge has to be classified according to all three criteria to assess the use options. For example, a class A1a sludge would be the best quality sludge which could be used in agricultural practices. However, due to the pollutant class of a class A1c sludge, agricultural use is not permissible. The document directs the reader to the appropriate Guideline volume to use based on the classification.
4 Volume 2: Requirements for the agricultural use of sludge Volume 2 describes the requirements and restrictions related to the safe use of sludge for the production of crops at agronomic rates (Snyman and Herselman, 2006ac). This volume is used when stabilised sludge is used as a nutrient source and/or soil conditioner at an application rate designed to supply a crop s nitrogen needs, while at the same time minimising the risk of nutrient leaching. This applies to both commercial as well as to small scale and subsistence farming practices. It can also be used to manage compost containing sludge that is not sold or distributed to the general public for use. This Volume details the management, technical and legislative aspects, as well as the sludge characterisation and monitoring requirements. It provides ceiling limits for metals and microbiological constituents in sludge intended for agricultural use, and encourages the implementation of vector attraction reduction options to stabilise the sludge. General and specific restrictions and requirements for the agricultural use of sludge are presented to minimise health risks and to protect the environment. Both sludge and soil metal limits are presented in this volume (Table 3 and 4). No soil metal restrictions apply for pollutant class a sludge and the use of pollutant class c sludge is not permissible. The soil metal limits detailed in Table 4 are only applicable when pollutant class b sludge is used in agricultural practices. If the total metal content of the soil is below the Total Investigation Level (TIL; Table 4), sludge of a pollutant class b can be applied and the situation re-assessed after five (5) years. If the total metal content of the soil is found to be higher than the Total Maximum Threshold (TMT; Table 4), sludge application is not permissible for this soil. The risk to the environment is unacceptable when the total metal content of the soil exceeds TMT. If the total metal content of the soil is found to be between the TIL and the TMT (Table 4) the mobility of the metals concentration in the soil needs to be assessed. The available metal content of the soil is determined using the NH 4 NO 3 extraction method (Snyman and Herselman, 2006ac). If the available metal content of the soil exceeds the Maximum Available Threshold (MAT, Table 4) level, pollutant class b sludge may not be applied on this soil. Table 3. Pollutant limits for the agricultural use of wastewater sludge in South Africa (Snyman and Herselman, 2006ac) Aqua regia extractable Pollutant class metals (mg/kg) a b C As < >75 Cd < > 85 Cr < > Cu < > Pb < > 840 Hg < > 55 Ni < > 420 Zn < > Note: A 90% compliance is required to comply with a pollutant class. If the available metal content of the soil is lower than the Maximum Available Threshold (MAT; Table 4), sludge of a pollutant class b can be applied and the situation re-assessed after two (2) years. After two years, the total and available metal content of the soil must be determined. If either of these results exceeds the TMT or MAT, the sludge application should be terminated.
5 Table 4. Limits for metals in soils (mg kg -1 ) (Snyman and Herselman, 2006ac) Total investigative level # (TIL) Total maximum threshold # (TMT) Maximum available threshold* (MAT) As Cd Cr Cu Hg Ni Pb Zn # - Total digestion method (Aqua regia, EPA 3051) * - NH 4 NO 3 extraction method Volume 3: Requirements for the on-site and off-site disposal of sludge Volume 3 describes the requirements and restrictions related to the on-site and off-site disposal of sludge (Herselman and Snyman, 2009ab). The Volume gives detailed requirements and guidance on managing the phasing out of unlined sludge stockpile facilities, operating existing dedicated land disposal sites; and, the rehabilitation and phasing out of dedicated land disposal sites. Other disposal options, such as off-site disposal of sludge in a general or hazardous landfill sites, on-site disposal of sludge in a mono disposal landfill or lagoon, and the disposal of sludge to the marine environment, are addressed in the context of other guidelines and policies published by the Department of Water Affairs and Forestry. Although the generic classification for the microbiological, stability and pollutant class remain the same (Table 1), a different set of limits and analytical method was adopted for the pollutant class in Volume 3. The pollutant class determination of sludge in Volumes 1 and 2 was based on the total metal content (aqua regia digestion) of the sludge. Since the total metal content of sludge does not give an indication of the potential leachability of the metals in the sludge, it is recommended that the pollutant class for disposal purposes be based on the leachable metal fraction in the sludge. The Toxicity Characteristic Leaching Procedure (TCLP) was adopted for this Volume (Table 5). The TCLP was developed in the USA by the Environmental Protection Agency to predict the leachate quality and hence the risk it poses to groundwater. In reference to this, South Africa has adopted the Estimated Environmental Concentration (EEC), which is a method whereby the exposure of aquatic fauna to constituents of concern in the waste is estimated and quantified. The TCLP test can be used to support/affirm the EEC (DWAF, 2006) and the potential of a waste to delist from a hazardous waste to a general waste. The recommended Pollutant class classification for sludge destined for land disposal is detailed in Table 5. Pollutant class a sludge (TCLP metal concentration AE) could be disposed on land without restrictions, but with monitoring requirements. When the analytical results of the TCLP test indicate Pollutant class b sludge, the sludge should be limed at a recommended dosage of 25mg lime /kg sludge. The TCLP test should be repeated on the sludge after liming. If the new results indicate Pollutant class a sludge, the sludge could be disposed on land as normal Pollutant class a sludge. In cases where the analytical results after liming still indicate Pollutant class b sludge, the load principle should be applied where the maximum load for the disposal area is calculated based on the TCLP concentration of the constituents of concern and more stringent management requirements would apply. Land disposal of Pollutant class c sludge would only be allowed on properly engineered lined disposal facilities with stringent management and monitoring requirements. Specific liming tests are recommended to achieve at least a Pollutant class b
6 classification. Table 5. Metal limits based on the TCLP test for the disposal of sludge TCLP extractable metals (mg/l) Pollutant class a b c AE >AE and 10*AE >10*AE Arsenic (As) >4.3 Cadmium (Cd) >0.31 Chromium (Cr III) >47 Chromium (Cr VI) >0.2 Copper (Cu) >1 Lead (Pb) >1 Mercury (Hg) >0.22 Nickel (Ni) >11.4 Zinc (Zn) >7 Volume 4: Requirements for the beneficial use of sludge Volume 4 of the Guidelines was developed with a view to maximise the beneficial use of sludge (Herselman and Moodley, 2009; Herselman, 2009). This Volume deals specifically with sludge application to land, for beneficial purposes, at rates higher than agronomic rates with specific management, technical and legislative aspects as well as restrictions and monitoring requirements to protect the receiving environment. It provides ceiling limits for metals and microbiological constituents in sludge intended for beneficial use and encourages the implementation of vector attraction reduction options to stabilize sludge. The volume deals with the restrictions and requirements for once-off high rate sludge, continious high rate application of sludge as well as the use of sludge as landfill cover. Once off application includes applications such as the rehabilitation of disturbed/degraded soils (nutrient depletion, erosion, acidity and salinity, poor physical properties, reduced biological activity) after mining activities, intensive farming and industrial activities and using sludge in the establishment of golf courses, race courses, vineyards, road embankments, public parks. If sludge is applied to the same piece of land more than three times at rates higher than agronomic rates, it will classify as continuous sludge application. Continuous high rate applications include the continuous application of sludge in natural forests and plantations, use of sludge as growth medium for plants, flowers and seedlings, cultivation of grain and fruit trees, cultivation of industrial crops (non-food crops) and instant lawn cultivation. Stabilised sludge can be used as daily and/or final cover on General or Hazardous landfill. Sludge with solids content of 50% looks and functions much like soil. It will increase the water holding capacity of the final cover of the landfill facility and has high odour absorbing abilities. Using sludge as cover material is, in essence, seen as co-disposal of sewage sludge with municipal solid waste on landfills. The metal limits (aqua regia extraction) for the once of and continuous high rate application of sludge on land is detailed in Table 3 (same as for the agricultural use of sludge) with specific metal limits for soils. The total metal concentration of the soil must be determined before high rate sludge application to determine whether additional metals can be added to the soil without negative effects on surface and groundwater. Limits have been set for metals in the receiving soil. These limits will depend on the present and future land-use of the site (agricultural or industrial) and are more stringent if the end land-use is agriculture (edible crops). The total maximum threshold (TMT) for metals in soil will protect soils destined for agricultural land-use and land with public access, while the
7 maximum permissible level (MPL) for metals in the receiving soil (Table 6) will protect industrial soils and land with limited public access to ensure that the soil quality does not degrade to such an extent that remediation would be necessary. Table 6. Metal limits for soil receiving high sludge loads (Herselman and Moodley, 2009; Herselman, 2009) Total Maximum Threshold (TMT) mg/kg Maximum permissible level (MPL) mg/kg As 2 20 Cd 3 5 Cr Cu Pb Hg 1 9 Ni Zn When the total metal content (aqua regia digestion) of the soil exceeds the TMT, sludge application on land where edible crops will be grown and/or where public access is unlimited is not permissible. In cases where the land is used to cultivate industrial crops, sites with limited public access and industrial areas (mine rehabilitation and forests) sludge may be applied. When the soil metal concentrations are higher than the MPL, sludge application is not permissible. The metal limits (TCLP) for the use of sludge as a landfill cover is detailed in Table 5 (same as disposal, Volume 3). Volume 5: Requirements for the thermal sludge management practices and for commercial products containing sludge Guidance on the thermal treatment of sludge was developed with a view to guide the sludge producer/user to the different thermal treatment options available for sludge (Herselman et al., 2009; Herselman, 2009b). The aim of incineration, also called combustion, is mainly to reduce the sludge volume through the conversion of the organic complexion of sludge to more basic compounds like carbon dioxide, oxides of nitrogen, water vapour, methane and hydrogen. Established thermal treatment processes include, but are not limited to: (1) Total or partial combustion of organic solids to oxidised end products (carbon dioxide and water) through incineration; (2) Partial oxidation and volatilisation of organic solids by pyrolysis or starved-air combustion to produce end products with energy content (e.g. methane, hydrogen, carbon monoxide); and (3) Co-incineration of sludge with other materials (municipal solid waste, wood waste and coal) in industrial processes such as industrial furnaces and cement kilns. Special attention is given to the legislative and technical aspects of thermal treatment, including air emission limits and air quality monitoring. These restrictions and requirements are presented to protect the receiving environment and the general public from any potential constituents of concern present in the sludge that may be present in air emissions. No metal limits are stipulated for the thermal treatment of sludge. However, a general risk-based equation  is proposed to determine the pollutant limits for sludge destined for complete combustion and co-combustion.
8 86400 C = CRSC DF (1 CE) SF Where: C = The pollutant limit (allowable daily concentration of As, Be, Cd, Cr, Pb, Hg or Ni in sludge, in mg/kg of total solids, dry-weight basis) CRSC = Chronic Risk Specific Concentration of a pollutant (the allowable increase in the annual average ground-level ambient air concentration for a pollutant at or beyond the property line of the site in µg/m³ DF = Dispersion Factor (in µg/m³/g/s, based on an annual average air dispersion model) CE = Sewage sludge incinerator control efficiency for As, Be, Cd, Cr, Pb, Hg or Ni (in hundredths, based on a performance test) SF = Sludge feed rate (in ton dry /day) = Time conversion factor (number of seconds per day) The second part of Volume 5 deals with management of commercial products containing sludge. This includes fertilizer products such as compost and pellets that are distributed to the general public for unrestricted use. To protect the receiving environment and the general public from any adverse effects of any constituents that may be present in the product, the quality of the final product should be regulated. The product must be sampled and analysed before distribution to the public and must comply with Class A1a according to its Microbiological class, Stability class and Pollutant class. The majority of commercial products (other than fertilizer) produced with sludge and/or incinerator ash as raw material are used in the construction business. This includes, but is not limited to, bricks, cement, pumice and artificial aggregate. Volume 5 also provides limited guidance on these aspects. IMPACT OF ADVANCED SLUDGE GUIDELINES IN A DEVELOPING COUNTRY South Africa, as a developing country, has progressive and comprehensive environmental legislation and guiding documents. Sadly, the implementation and regulation fail in some cases. Although the sludge guideline series were well received by the authorities and industry, it is important to establish whether the intended objectives will be achieved in the medium to long term. An assessment was done on the current and potential future impacts of the South African Guidelines for the Utilisation and Disposal of Wastewater Sludge, on socio-cultural, economic, health and environmental aspects of South African society (Van der Waal, 2006). The aim of this work was to quantify the potential impact of the Sludge Guidelines on South African society by analysing current examples of wastewater sludge best practice that are aligned with the new Sludge Guidelines. The impact of the new sludge guidelines on human health was not quantified as this is difficult to isolate from the impacts of other social conditions such as poverty and HIV/Aids. The study showed positive economic impact of the use of sludge in land application, brick manufacturing, composting and fertiliser manufacturing. Economic benefits were either in the form of profitable private enterprises or local authorities reporting significant savings when applying sludge beneficially (Van de Waal, 2008). In terms of the social impact, the potential for job creation was quantified in 6 small enterprises which created 36 semi-skilled and skilled jobs (often the sole breadwinners within their families and communities). If companies across South Africa were established to take advantage of sludge re-use the social impact would be significantly more than what is outlined in the 6 case studies investigated during the impact assessment. The 
9 environmental impact was quantified in terms of avoidance of the deterioration of land to the extent that rehabilitation is required. Negative environmental impacts have resulted largely from unsustainable sludge handling and mismanagement practices. These can be avoided in future through the application of the new Sludge Guidelines. It is recognised that the implementation of the guidelines do not come without the costs of implementation and operation. However, it is clear from this impact study that each aspect, namely economy, society, environment and to a certain extent human health, will potentially be impacted positively if the new South African Guidelines were fully implemented. CONCLUSIONS The release of the new South African Wastewater Sludge Guideline series aims to rectify previous sludge guideline shortcomings and provide an easy to use management tool for the handling of wastewater sludge in this developing country. This paper presents an overview the sludge management practices in South Africa and provides a summary of the content of the newly developed South African Sludge Guideline Series developed to encourage sustainable sludge management. The three tier sludge classification system includes microbiological limits, stability criteria and pollutant limits is presented. Specific discussions regarding the metal limits for each use are presented. These guidelines are therefore now being implemented and field data will present interesting trends regarding the validity of these guidelines. In the short term an impact assessment was done to assess the current and potential future impacts of the South African Wastewater Sludge Guideline series on socio-cultural, economic, health and environmental aspects of South African society. REFERENCES DWAF, Waste Management Series. 3rd Edition. Minimum Requirements for the Handling, Classification and Disposal of Hazardous Waste. Herselman J. E. (2009a). Technical Support Document to the Development of the South African Sludge Guidelines: Volume 4: Requirements for the Beneficial Use of Sludge at High Loading Rates. Water Research Commission K5/1622/2/09, Pretoria, South Africa. Herselman J. E. (2009b). Technical Support Document to the Development of the South African Sludge Guidelines: Volume 5: Requirements for Thermal Sludge Management Practices and for Commercial Products Containing Sludge. Water Research Commission K5/1622/3/09, Pretoria, South Africa. Herselman J. E., Burger L. W. and Moodley P. (2009). Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 5 of 5: Requirements for Thermal Sludge Management Practices and for Commercial Products Containing Sludge. Water Research Commission TT 351/09, Pretoria, South Africa. Herselman J. E. and Moodley, P. (2009). Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 4 of 5: Requirements for the Beneficial Use of Sludge at High Loading Rates. Water Research Commission TT 350/09, Pretoria, South Africa. Herselman J. E. and Snyman H. G. (2009a). Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 3 of 5: Requirements for the On-site and Off-site Disposal of Sludge. Water Research Commission TT 349/09, Pretoria, South Africa. Herselman J. E. and Snyman H. G. (2009b). Technical Support Document to the Development of the South African Sludge Guidelines: Volume 3: Requirements for the On-site and Off-site Disposal of Sludge. Water Research Commission K5/1622/1/09, Pretoria, South Africa. Pandit, M. and Das, S. (1998) Sludge Disposal. Water treatment primer: CE4124: Environmental Information Management. Civil Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA. Snyman, H.G. (2007) Management of wastewater and faecal sludge in Southern Africa. In Proc. of the IWA Specialist Conference, Moving Forward wastewater Biosolids Sustainability: Technical, Managerial, and public synergy, Moncton, Canada, June.
10 Snyman, H.G., Forsmann, P and Smollen, M The feasibility of electro-osmotic belt filter dewatering technology at pilot scale. Water Sci. Technol 41 (8): Snyman H. G. and Herselman J. E. (2006a). Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 2 of 5: Requirements for the Agricultural Use of Wastewater Sludge. Water Research Commission TT 262/06, Pretoria, South Africa. Snyman H. G. and Herselman J. E. (2006b). Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 1 of 5: Selection of Management Options. Water Research Commission TT 261/06, Pretoria, South Africa. Snyman H. G. and Herselman J. E. (2006c). Premise for the Development of Volume 1 and 2 of the South African Sludge Guidelines. Water Research Commission K5/1453/1/06, Pretoria, South Africa. Snyman, H.G., Van Niekerk, A.M., Herselman, E. and Wilken, J.W. (2006) Development of the South African wastewater sludge guidelines. Water Sci. Technol. 54 (5): Snyman, H.G., Herselman, J.E. and Kasselman, G. (2004). A metal content survey of South African sewage sludge and an evaluation of analytical methods for their determination in sludge. WRC Report no: 1283/1/04. ISBN , South Africa. Van der Waal C. (2008). Guidelines for the Utilisation and Disposal of Wastewater Sludge: Volume 1-5, Impact Assessment. Water Research Commission TT 370/08, Pretoria, South Africa. WRC. (1997) Department of Agriculture, Department of Health, Department of Water Affairs and Forestry, Water Institute of Southern Africa, Water Research Commission. Permissible Utilisation and Disposal of Sewage Sludge. 1st Edition. TT85-97 Pretoria. Water Research Commission. WRC. (2002) Department of Agriculture, Department of Health. Department of Water Affairs and Forestry. Water Research Commission. Sludge Consultant. Addendum No, 1 to Edition 1 (1997) of Permissible Utilisation and Disposal of Sewage Sludge. TT 150/01 Pretoria. Water Research Commission.