The application of composting for phosphorous recovery from alum and ferric precipitated sludges
Date
2024-04-28
Authors
Vahedi, Saba
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Abstract
In this study, the recovery of phosphorous (P) from sludge produced during phosphorous removal
from secondary wastewater lagoons by using a controlled composting process was investigated.
Two compost piles, one using Alum (Al) and the other Ferric (Fe) precipitated sludge, were
established. Sludge was mixed with dry woodchips (1:3 ratio), manually turned weekly, and
monitored for temperature, moisture, and pH, every two days. After an eight-week thermophilic
phase and six-week maturity phase, compost met Category A criteria per CCME guidelines. The
compost products were tested on switchgrass and canola to assess phosphorus availability, with
control experiments using topsoil and Monoammonium Phosphate (MAP) fertilizer. Three
cropping cycles, each lasting 50 days, were completed, and analysis of harvested biomass for total
phosphorus content using the Inductively Coupled Plasma (ICP) method was conducted.
The analysis of the data showed that the phosphorus source with the greatest P uptake and biomass
yield for switchgrass was Ferric Compost. Across different growth cycles, P uptake increased for
all phosphorus sources, indicating a gradual release of P from composted chemical sludge over
time through mineralization. In terms of canola, Fe compost was the most effective phosphorus
source in promoting P uptake. P uptake increased steadily throughout growth cycles when
cultivating canola with MAP. However, P uptake decreased with Al compost and Fe compost as
growth cycles progressed. Regarding canola, among the three phosphorus sources, Al Compost
resulted in the highest biomass yield for all phosphorus sources, while biomass yield decreased as
growth cycles progressed. Overall, Fe compost proved most effective for P uptake and biomass
yield in switchgrass, while Al compost showed better results for canola. Furthermore, the
evaluation of phosphorus recovery efficiency (PRE %) underscored the fluctuating nature of
phosphorus retention in both switchgrass and canola
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Keywords
Composting, Chemical precipitated sludge, Phosphorus recovery, Canola, Switchgrass