Environmental Engineering Reference
In-Depth Information
Parameter weighted average per
treatment
ΔVSS ΔNO
x
-N
Y
(ΔVSS/
Treatments
(Sampling time)
(mg/L)
(mg/L) ΔNO
3
-
-N)
VSS produced
NO
3
-
-N removal
(g/g)
kg/d
kg/m
3
d
kg/d
kg/m
3
d
1 & 2 (2:00 p.m.)
9.17
7.49
1.24
1 & 2 (10:00 p.m.)
23.65
26.99
0.88
0.303
20.203
0.351
23.407
1 & 2 (6:00 a.m.)
27.50
29.40
0.94
3 & 4(2:00 p.m.) 6.50 4.18 1.58
3 & 4 (10:00 p.m.) 18.84 19.57 0.96 0.237 15.797 0.243 16.198
3 & 4 (6:00 a.m.) 18.67 19.91 0.95
Table 12. Biological yields (
Y
NO3-N
) data from denitrification reactor (steady state conditions)
for each experimental working flow, VSS produced, and NO
3
-
-N removal.
higher reaction rates. Furthermore, these conditions could imply even higher nitrogen
removal if recycling did not have to be employed in order to assure bed fluidization.
Additionally, the reactor maintained a high VSS biomass concentration, around 38,000
mg/l. Under these conditions, the sand from the settled media on average represented only
17% of the settled bed volume in the reactor. This information would be critical for the
design of sand denitrification filters to be operated under similar conditions.
3.10 Estimation of operations costs for wastewater treatment at BRA
Experimentation with the pilot station showed that by using these treatment strategies, water
quality can be improved to the degree that treated effluent is safe for fish production. The
commercial feasibility of effluent treatment and reuse, however, depends upon an assessment
of benefits and costs. Estimation of the construction costs for a full-scale wastewater treatment
station based on the pilot-scale design that we evaluated is beyond the scope of our study.
Further, amortization of capital costs is highly variable among countries and times and hence
is not well given to useful discussion. Operating costs, however, are estimable using data
available to us. Operation of a scaled-up plant treating the entire BRA effluent of 2260 m
3
/day
would require electricity, oxygen for ozone production, methanol as a substrate for
dentrification, ferric chloride for flocculation, and labor for operations and maintenance.
We assumed an ozone dose of 0.1 g/l wastewater, about 15% higher than the dose applied
in treatment 3, the most successful treatment during pilot station experiments. Results of the
pilot-scale study showed that such an increase should be economically feasible. This dose
represents a total of 226 kg O
3
/day. At an average of 12.14 kWh consumed per kg of ozone
produced, the energy required daily will be 2743.6 kWh. At a local market price of
$0.04/kWh, the costs of producing ozone will be US$110/day. Considering that the
electricity required to operate the station is 10% of the energy required to produce ozone,
total costs for electricity would be $120.75/day.
With current technology, which is capable of transforming 12% of oxygen into ozone,
1652.87 m
3
of oxygen will be needed to produce the daily amount of ozone applied (i.e., 1.17
m
3
O
2
/min). This volume is equivalent to 2257.6 kg O
2
(at 1.43 kg O
2
/m
3
). Assuming oxygen
recirculation and a supplemental loss of oxygen due to dissolution in water, oxygen
consumption should be approximately 10% of the amount used. Hence, the cost of 225.8 kg
of oxygen consumed daily will be $15.50/day, at a bulk price of $0.092/m
3
.
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