1. Grisales, D.K., Ortega, L.J., Chaparro, R.T
Treatment of hospital wastewaters by ozone: preliminary evaluation.
Grisales, D.K., Ortega, L.J., Chaparro, R.T
Sanitation Laboratory, Civil Engineering Department, Military University, Bogota (Colombia). Carrera 11 No 101 – 80
Introduction
The emerging pollutants have defined as a group of compounds that interfere with the functioning of endocrine systems. In most cases emerging contaminants correspond to unregulated pollutants, which may be candidates for future regulations. Hospital Wastewater (HWW) represents one of the most ubiquitous water sources in the total urban water cycles, where the generated effluents are usually loaded with pharmaceutical, chemical, radioactive and other toxic chemical substances, as well as various pathogenic microorganisms (Rezaee et al. 2005). Hospital wastewaters are normally discharged directly without pre-treatment to sewers. Despite mostly being only a small fraction of the total wastewater volume in the influent of a sewage treatment plants (STP), Hospital wastewater has gained increasing scientific and public attention in the last decade. This is part due to the HWW is considered as the major source of undesirable constituents. Several studies have demonstrated that the typical constituents of the HWW (i.e antibiotics, anaesthetics, disinfectants, heavy metals) are not removed on conventional treatments, as a result may be founded on water sourced and can be related with environmental risks on human health. To our knowledge, only a few publications are related to the treatments of real HWW, the studies generally are limited to a synthetic hospital wastewaters or specific compounds. Moreover, studies on ecotoxicological impact of HWW are scarce.
Objective
In our study real hospital wastewater was used to evaluate the effect of ozone at different initial pH. Moreover, was studied the total toxicity using bulbs of Allium cepa L as bioindicator, before and after ozone application. This work could contribute practical knowledge for the treatment of real HWW using ozone as a pre-treatment of subsequent biological process.
Experimental
Central Military Hospital (Bogota – Colombia)
Real Hospital Wastewater
Table 1. Parameters evaluated
Treatment
Parameters
Units
References
Ozone
COD
mg/L
APHA (2005)
BOD
UV254
1/cm pH
---
Residual ozone
mg O3/L
Total toxicity
% inhibition on the growth of roots of
Allium cepa L.
Fiskesjo (1993)
Table 2. Operational conditions of ozone application.
Ozone Reactor
Ozone application
Production
188 mg.h-1
Reaction time (min)
15, 30, 45, 60
Volume
1000 mL pH
pH = 3,0 – pH = 10, pH = without modification (6,7)
Figure 1. Schematic of the wastewater treatment
Wastewater was obtained from the Central Military Hospital (CMH) located in Bogotá (Colombia). The CMH has a total of 1100 beds, 350,000 patients are served and offers all services of a modern hospital. Wastewaters are released into the main sewer of the Hospital from where it joins the city’s sewerage system. Thus, the samples from this hospital were collected from the main sewer. The effluents were collected 4 times during the year 2011.
Results
Effect on Biodegradaility
Table 2. Characteristics of the Hospital Wastewater
The results in this study showed that the ozonation promotes the enhanced of the biodegradability of the HWW for the experiments conducted under different initial pH.
For pH = 3.0, COD/BOD increased in 40%. The increased biodegradability was caused by an increase in BOD5 and concomitant decrease in effluent COD (48 – 58%).
At pH = 10 the biodegradability ratio increase in 71%, and this was consequence of the increase of BOD5 in 40% and a slight COD decrease.
In both cases the increase in BOD5 provided the dominant contribution to the biodegradability enhancement considering that COD decreased to a very limited extend.
Parameters
Units
Mean± S.D pH
---
6.7±0.5
Alkalinity
mg/L
375±93
Chloride
mgCl-/L
153±40
Total Solids
412±143
COD
310±123
BOD5
46±37
COD/BOD5
----
7.6±4.3
UV254
cm-1
0.67±0.4
VIS436
0.1±0.1
SO4-2
19±3.1
TKN
7.2±1.5
PO4-2
8.6±1.8
Faecal Coliform
CFU/mL
3.1 x 106±2,3 x 106
Effect on Toxicity
In our study we founded that the CMH wastewater without treatment results in an inhibition on the root growth of 69% and after ozone dose of 187 mgO3/L and pH = 10 the inhibition percentage was reduced to 18%. In particular, ozonation at basic conditions resulted in a reduction of the total toxicity in 62%.
It is worth mentioning that not much work has been carried out about the treatment of real HWW, thus the present study presents valuable knowledge about this type of effluents and the effects of ozone application.
Figure 2. UV254 and VIS436 and applied ozone dosage
*S.D: standard deviation, n=4
Conclusions
The effect of ozonation at different initial pH and its impact on the total toxicity of real hospital wastewater was studied in this work. The results have demonstrated that the ozone application under different initial pH improves the hospital wastewater quality. At basic conditions the biodegradability ratio increases in 71% with an ozone dosage of 187 mgO3/L. However, at acidic conditions were founded the highest removal efficiency of UV254 and Colour (VIS436) In the case of the total toxicity the ozone promoted a reduction of 62% at basis conditions. In general, the military hospital wastewater varied considerably, thus the results in some cases were inconsistent, indicating the requirement of additional studies for a whole monitoring of the water quality.
References
APHA. (2005). Standard Methods for the Examination of Water and Wastewater 21th. ed. American Public Health Association/American Water Works Association/Water Environment Federation, Washington,DC,USA. Fiskesjo, G. (1993). Allium test: A 2-3 day plant test for toxicity assessment by measuring the mean root growth of the onions (Allium cepa L).Environmental Toxicology and Water Quality: An International Journal, 8, Rezaee, A., Ansari, M., Khavanin, A., Sabzali, A., Aryan, M.M. (2005). Hospital wastewater treatment using an integrated anaerobic-aerobic fixed film bioreactor. American Journal of Environmental Sciences, 1 (4) ,
References