The 5-step management framework for the control of _Ascaris_ risks is as follows: _Step 1: Define the tolerable maximum additional burden of disease_ This is taken as 10<sup>−4</sup> DALY loss pppy, as for viral, bacterial and protozoan pathogens. The current global DALY loss due to ascariasis is 1.8 × 10<sup>−3</sup> pppy, so accepting a tolerable additional burden of ascariasis from wastewater use in agriculture of 10<sup>−4</sup> DALY loss pppy means that the burden of ascariasis would increase from 0.0018 to 0.0019 DALY loss pppy, which is not epidemiologically significant (Mara and Sleigh 2010c).

_Step 2: Derive tolerable disease and infection risks_ As determined in section A.4 of Annex A, and using an _Ascaris_ disease/infection ratio of 1 (i.e., all those infected with _Ascaris_ develop ascariasis), the tolerable _Ascaris_ infection risk is 1.2 × 10<sup>−2</sup> pppy.

_Step 3: Conduct QMRA-MC risk simulations to determine required minimum total_ Ascaris _reductions for both restricted and unrestricted irrigation_ This step is broadly the same as Step 3 for viral, bacterial and protozoan pathogens (section 4.2.1), but the QMRA-MC _Ascaris_ programs for restricted and unrestricted irrigation are now run, with locally appropriate parameter ranges, for ranges of _Ascaris_ egg numbers (rather than assuming pathogen numbers per 10<sup>5</sup> _E. coli_ ) —for example, 100−1000 eggs per liter of wastewater (unrestricted irrigation) or per kg of soil (restricted irrigation), 10−100 eggs per liter or kg, and 1−10 eggs per liter or kg. Then the QMRA-MC _Ascaris_ program for un- restricted irrigation is run.<sup>22</sup> These QMRA-MC results then show the log unit _Ascaris_ reductions which ensure that the tolerable maximum _Ascaris_ infection risk of 1.2 ×10<sup>−2</sup> pppy is not exceeded.

_Step 4: Determine how the required pathogen reduction is to be achieved_ _Step 5: Verification monitoring_ Steps 4 and 5 are the same as Steps 4 and 5 for viral, bacterial and protozoan pathogens (section 4.2.1).

# **4.3 Options for reducing microbial risks**

# _4.3.1 Wastewater treatment_

As detailed in sections A.3 and A.4 of Annex A, norovirus and _Ascaris_ reductions of 3−4 log units are required to not exceed a maximum additional burden of disease of 10<sup>−4</sup> DALY loss pppy. Thus wastewater treatment could be required to achieve only a 1−2 log-unit reduction, with the remaining 1−3 log units being achieved by post-treatment health-protection control measures.

# _Viruses, bacteria, protozoa_

_2-log unit reduction:_ wastewater treatment to produce a 2-log unit reduction can be achieved by simple treatment processes, such as an anaerobic pond (or equivalent anaerobic reactor) followed by either a facultative pond or a subsurface horizontal-flow constructed wetland.<sup>23</sup> _1-log unit reduction:_ wastewater treatment to produce a 1-log unit reduction can be readily achieved by very simple treatment processes, such as an anaerobic pond, a three-tank or three-pond system, or overnight settling. The three-tank (or three-pond) system is operated as a sequential batch-fed

> 22 See Mara and Sleigh (2010d) for practical details on running QMRA-MC programs; Tables A.8 and A.10 in Annex A show typical simulated _Ascaris_ infection risks.

> 23 See Mara (2004) for design details.

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