Removal of phosphorus from wastewaters by biomass
ashes
R. Barbosa, N. Lapa, H. Lopes, A. Morujo and B. Mendes
ABSTRACT
Removal batch assays of phosphates from a synthetic wastewater (SWW) and a pulp and paper
mill wastewater (PPWW) with two forestry biomass ashes were performed. The supernatants were
not only chemically characterized but also the ecotoxicity was determined using two organisms:
Vibrio fischeri and Artemia franciscana. The addition of fly ash and bottom ash to the SWW in
solid/liquid (S/L) ratios of 3.35 and 9.05 g L
1
, respectively, achieved removal percentages of
phosphates >97% for both ashes. The addition of fly ash and bottom ash to the PPWW in S/L ratios
of 34.45 and 46.59 g L
1
, respectively, yield removal percentages of phosphates >90% for both
ashes. According to the results of the Langmuir and Freundlich isotherms, the removal of
phosphates from the SWW was mainly explained by surface removal mechanisms, while the
removal from the PPWW was partially explained by multi-layer mechanisms. The supernatants
resulting from the treatment of SWW and PPWW with both biomass ashes did not present
acute ecotoxicity.
R. Barbosa
N. Lapa (corresponding author)
A. Morujo
B. Mendes
Faculdade de Ciências e Tecnologia,
Department of Sciences and Technology of
Biomass,
Universidade Nova de Lisboa,
Campus da Caparica, Edifício Departamental,
Piso 3, gab. 364,
2829-516 Monte da Caparica,
Portugal
E-mail: ncsn@fct.unl.pt
H. Lopes
Laboratório Nacional de Energia e Geologia,
Unidade de Tecnologias de Conversão e
Armazenamento de Energia,
Campus do Lumiar, Estrada do Paço do Lumiar, 22,
1649-038, Lisboa,
Portugal
Key words | biomass ashes, ecotoxicity, pulp and paper mill wastewater, removal of phosphates
INTRODUCTION
Several chemical and biological treatment processes to
remove P from wastewaters have been studied in recent
years (Wood et al. ; Pratt & Shilton ). Within the
group of chemical processes, the use of residues to remove
P from wastewaters has been attempted in several works
(for example, Yang et al. ). This is an interesting topic,
because of the high P-adsorption capability of some sub-pro-
ducts and their low cost.
Nevertheless, some sub-products require a previous
thermal activation before their use as efficient adsor-
bents, increasing the cost of the final adsorption
product (Xiong et al. ). Hence, the reuse of sub-
products from thermal processes would be much more
interesting, because they avoid the thermal activation
pre-treatment. The use of ashes resulting from the for-
estry biomass power plants (biomass ashes) becomes in
this context a very interesting issue, because they have
high concentrations of active Ca, Al, and Fe that can
participate in phosphate removal. Moreover, heavy
metals are present in trace or even undetectable concen-
trations in these ashes (Ahmaruzzaman ; Singh et al.
).
The main objectives of this work were to (i) study the
potential of biomass ashes to remove phosphates from
both a synthetic wastewater (SWW) and a pulp and paper
mill wastewater (PPWW) and (ii) assess the ecotoxicity
impact caused by the addition of these ashes to both
wastewaters.
MATERIAL AND METHODS
Origin and characterization of biomass ashes
Two types of biomass ashes were used in this study: fly and
bottom ashes. They were collected in a biomass power plant
that produces electricity by burning forestry residues (bark
of eucalyptus and pine). The bottom ash was collected in
the bottom of the furnace and fly ash was collected in the
bag-house filters. In a previous work (Barbosa et al. ),
both biomass ashes were characterized for (i) particle size
distribution (ISO 3310-2 ) and (ii) chemical compo-
sition through acidic digestion (USEPA Method 3051A
).
2019 © IWA Publishing 2013 Water Science & Technology | 68.9 | 2013
doi: 10.2166/wst.2013.455