Water Journal : Water Journal August 2012
refereed paper biosolids water AUGUST 2012 71 Abstract Land application of biosolids is an important component of beneficially using solid wastes from sewage treatment processes. The aim of many water authorities is to achieve 100% beneficial use of biosolids. To achieve this, repeat application of biosolids to the same site nearby is a useful strategy, as transport costs are minimised and fertiliser requirements at the site of application can be met while improving soil organic matter content. A one-in-five-year "repeat application tradition" is generally practiced across the water industry in Victoria. This "one-in-five-year norm" anecdotally seems to have originated from the world's best management practices during the earlier stages of schemes involving land application of biosolids, as a conservative approach. However, there appears to be no one regulatory document available that states this 'rule'. Our knowledge and understanding of biosolids' chemical and physical risks (beneficial and detrimental) has improved considerably over the last few decades and it is time to reconsider the guidance offered for the practice of beneficial land application of biosolids. This paper reviews the current Australian and overseas regulations governing repeat application of biosolids, and the set of rules that govern repeat applications, and defines what is currently considered best practice. Recommendations as to revisions and improvement of the current guidance for beneficial land application of biosolids is suggested as a first step in embracing a transparent risk-assessment-based strategy for the future. Introduction Land application of biosolids continues to play an important role in the beneficial use programs, mainly because of its relatively low cost of recycling the nutrients and addition of much-needed organic matter to soils. In the south-east region of Melbourne, biosolids are produced at treatment grade T1 and contaminant grade C2 (see EPA Victoria, 2004 for grading details). The preference to date has been for application on agricultural land adjacent to sewage treatment plants (STPs) owned by water authorities -- for example, South East Water Corporation in Victoria applies biosolids produced at Pakenham STP, Koo Wee Rup STP, Lang Lang STP, Boneo STP, Somers STP and Mt Martha STP to land at various agricultural (fodder production and cattle grazing) and landscaping sites. For the past 11 years (2001 to 2011), biosolids have been applied on South East Water Corporation-owned land for agriculture with an average use of 127% of biosolids currently produced each year. The annual target for the beneficial use of biosolids is 105% of the current year's production to ensure that some of the current stockpiles are used. The Victorian EPA expects water authorities to achieve 100% reuse to ensure no long-term accumulation of biosolids. Repeat applications of biosolids on the same land is common practice in Victoria (e.g., South East Water). The reasons for this are varied and typically include: • Lack of availability of suitable land near the STP, meaning repeat applications are more cost effective than seeking land further away; • The risk-adverse nature of the water industry, leading to an avoidance of applying biosolids onto land owned by third parties, thus further limiting available land for reuse; and • A reputed agricultural value of providing further nutrients and organic matter. A one-in-five-year "repeat application tradition" is generally practiced across the water industry in Victoria. This "putative one-in-five-year norm" ostensibly originated from world's best management practices during earlier stages of biosolids beneficial use schemes, as a conservative approach. This intent was seemingly to ensure biosolids applications do not result in significant accumulation of heavy metals, especially cadmium (Cd), in soils. For example, the Victorian EPA guidelines (EPA Victoria, 2004) are silent on this 'rule', except to suggest a need to assess soil contaminant concentrations before repeat application is carried out. This is primarily to ensure receiving soil contaminant 'levels' are always below the Receiving Soils Contaminant 'Limits' (RSCLs). It is also possible that the "one- in-five-year norm" in Victoria originated from the cadmium loading rate rule that limits the application of biosolids to 150g cadmium/ha/5 years (EPA Victoria, 2004). D Stevens, A Surapaneni, N Albuquerque, B Meehan, D Smith, P Uren, P Hansen A review of the current Australian guidelines REPEAT APPLICATION OF BIOSOLIDS ON AGRICULTURAL LAND Table 1. General rules to be met prior to land application of biosolids across Australia. No. Rule 1 Nutrient (N, P and K) Limiting Application Rate (NLAR) Rule Nutrients must always meet crop requirements (agronomic rate). 2 Soil Contaminant Rule The receiving soil's contaminant 'levels' must not exceed the Maximum Soil Concentration (MSC) or Receiving Soils Contaminant Limit (RSCL) set by guidelines. 3 Maximum Application Rate Rule The maximum allowable application rate should be the lower rate of the nutrient (NLAR) and contaminant (Contaminant Load Application Rate, CLAR) application rates. 4 Time Limiting Cadmium Loading Rate Rule The biosolids application rate must not exceed the cadmium loading rate of "30g/ha/yr averaged over five years or 150g/ha/5 years". 5 Soil pH Rule Biosolids should not be applied to soils having a low pH without appropriate safeguards (e.g., lime addition to low-pH soils). 6 Residual Soil N Rule Residual nitrogen in soil should also be determined and taken into account in calculating the application rate.
Water Journal September 2012-1
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