Variations in BOD, algal biomass and organic matter biodegradation constants in a wind-mixed tropical facultative waste stabilization pond.
This study considered the impact of wind mixing on the efficiency of BOD removal and the first order biodegradation constant for organic matter in a primary facultative pond. Wind speeds of 1-4 m/s blowing from the effluent end of the pond towards the influent created surface-water flows of up to 0.94 m/s as determined by orange and coconut drogues moving in the opposite direction to the bulk hydraulic flow of 0.217 m/s. This was sufficient to cause mixing of the water column resulting in loss of stratification in terms of chlorophyll a, temperature and dissolved oxygen. BOD and chlorophyll a concentrations were spatially and temporally homogeneous throughout this large pond. BOD removal efficiency was only 50.30% as opposed to a projected value of 79% despite an acceptable surface organic loading of 350 kgBOD5/ha/d and an actual k value for BOD removal using influent sewage samples of 0.29 d-1 close to the projected value of 0.30 d-1. It would seem that wind mixing reduced pond efficiency by destroying stratification and thus reducing the microbial activity necessary to consume organic material. Mixing also increased the mean chlorophyll a concentration compared to stratified facultative ponds receiving similar loads and non-motile algae dominated the water column.
Meneses
C G R
CG
Department of Chemical Engineering, Federal University of Rio Grande do Norte, Natal, Brazil. carlagracy@eq.ufrn.br
Saraiva
L B
LB
Melo
H N de S
HN
de Melo
J L S
JL
Pearson
H W
HW
D001673:Biodegradation, Environmental; D018533:Biomass; D019149:Bioreactors; D002734:Chlorophyll / Q000032:analysis / Q000378:metabolism; D000077194:Chlorophyll A; D056890:Eukaryota / Q000378:metabolism*; D005160:Facility Design and Construction; D007700:Kinetics; D009930:Organic Chemicals / Q000378:metabolism*; D012722:Sewage / Q000737:chemistry / Q000382:microbiology*; D014329:Tropical Climate; D014865:Waste Disposal, Fluid / Q000379:methods*; D014872:Water Movements; D018508:Water Purification / Q000379:methods*; D014919:Wind
D009930:Organic Chemicals; D012722:Sewage; D002734:Chlorophyll; D000077194:Chlorophyll A