Sanitizing Fecal Sludge for Reuse Using Wood Ash as an Additive
Sanitizing Fecal Sludge for Reuse Using Wood Ash as an Additive
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Date
2015-10-20
Authors
Monney, Isaac
Awuah, Esi
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Publisher
recycling
Abstract
Wood ash has been widely used as an additive for excreta from dry compost
toilets to sanitize it for reuse. However, there is dearth of quantitative information about its
efficiency in sanitizing partially digested sludge from wet onsite sanitation systems.
This paper presents findings of a series of two experimental studies to assess optimum
wood ash dosages required to raise the pH of partially digested fecal sludge to sanitizing
levels (pH > 11) in a tropical climate. The study monitored the variation of pH of the
sludge containing between 0 (control) and 180 g of ash per litre of sludge. Average initial
pH and total solids of the sludge were 7.79 and 72 g/L respectively. Generally,
the magnitude and rapidity of pH spike was correlated with the ash dosage (r = 0.988) and
was statistically significant (p = 0.0015; Fcrit = 2.3157) among all dosages. Drastic increase
in pH (from 7.81 to 11.60 ± 0.07) was recorded in the first 24 h for ash dosages between
140 g/L and 180 g/L, whereas dosages below 140 g/L had pH values less than 10.
The difference in variation of pH between the first 24 h and the successive 24 h was
statistically significant (P(T ≤ t)two-tail = 0.00; tcrit = 2.09). On the average, 97% of the
overall pH increment within a 48-h monitoring period occurred in the first 24 h for the
140–180 g/L ash dosages. The optimum ash dosages are 7–15 times higher than reported
lime dosages but ash provides a cheaper alternative than lime for recycling plant nutrients.
Further studies on pathogen inactivation efficiency are ongoing.
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Citation
Monney, I., & Awuah, E. (2015). Sanitizing fecal sludge for reuse using wood ash as an additive. Recycling, 1(1), 14-24.