Characteristics of hospital wastewater

In hospital a variety of substances besides pharmaceuticals are in use for medical purposes asdiagnostics and disinfectants. Besides the active substances, formulation adjuvants and in some instances, pigments and dyes are also drug components. Disinfectants, in particular are often highly complex products or mixtures of active substances. After application, many drugs are excreted non-metabolised by the patients and enter into wastewater. After their use and disinfectants also reach the wastewater. The different substances, which are not biodegradable, may finally enter surface water by wastewater treatment plants effluents and enter groundwater after the application of sewage sludge as fertilisers. The composition of the wastewater from Sevom Shabanhospital is presented in Table 1. Hospitals consume an important volume of water a day. In Sevom shaban hospital, the average needs in water was estimated at 1000 L/bed/day. Indeed the consumption of domestic water, is on average 100 L/person/day, while the value generally admitted for hospitals varies from 400 to 1200 L/day/bed. In France, the average needs in water of a university hospital center is estimated at 750 L/bed/day. This important consumption in water of hospitals gives significant volumes of wastewaterloaded with microorganisms, heavy metals, toxic chemicals and radioactive elements. As a result the hospitals generate hybrid wastewater, at the same moment domestic, industrial and effluents of care and medical research. Efficient treatment of hospital sewage should include the following operations:

  1. Primary treatment,
  2. Secondary biological purification; Most helminths will settle in the sludge resulting from secondary purification, together with 90-95% of bacteria and a significant percentage of viruses; the secondary effluent will thus be almost free of helminths, but will still include infective concentrations of bacteria and viruses,
  3. Tertiary treatment; The secondary effluent will probably contain at least 20 mg/L suspended organic matter, which is too high for efficient chlorine disinfection. It should therefore be subjected to a tertiary treatment, such as lagooning; if no space is available for creating a lagoon, rapid sand filtration may be substituted to produce a tertiary effluent with a much reduced content of suspended organic matter (<10 mg="" l="" li="">
  4. Chlorine disinfection; To achieve pathogen concentrations comparable to those found in natural waters, the tertiary effluent will be subjected to chlorine disinfection to the This may be done with chlorine dioxide (which is the most efficient), sodium hypochlorite, or chlorine gas. Another option is ultraviolet light disinfection. Disinfection of the effluents is particularly important if they are discharged into coastal waters close to shellfish habitats, especially if local people are in the habit of eating raw shellfish.

The sludge from the sewage treatment plant requires anaerobic digestion to ensure thermal elimination of most pathogens. Alternatively, it may be dried in natural drying beds and

then incinerated together with solid infectious healthcare waste. On-site treatment of hospital sewage will produce a sludge that contains high concentrations of helminths and other pathogens. According to the relevant WHO guidelines, the treated wastewater should contain no more than one helminthes egg per litre and no more than 1000 faecal coliforms per 100mL if it is to be used for unrestricted irrigation. The sludge should be applied to fields in trenches and then covered with soil. Integrated anaerobic-aerobic fixed-film reactor with arranged media, fed with hospital wastewater, achieved organic matter removal efficiencies of 95.1%. These results were consistent with the conclusions obtained by other working with integrated anaerobic/aerobic bioreactor, who pointed out that the main function of the non-aerated zone was the conversion of slowly biodegradable matter into short chain fatty acids, easily oxidized in the anoxic and aerobic processes. Anyway, it is possible that the anaerobic COD removal was underestimated because a part of methane was probably stripped in the aerobic zone. Organic matter concentration in the effluent was approximately constant, around 450 mg/l COD and 270 mg/l BOD5, independent from feed concentration and organic loading rate. Consequently, it can be considering that organic matter removal takes place simultaneously by aerobic oxidation, anoxic and anaerobic processes. It was found out that most of the COD was removed through aerobic oxidation (85%), while the anaerobic removal stood only for 15%. Theseresults were consistent with the conclusions obtained by other working with integrated anaerobic-aerobic bioreactor, who pointed out that the main function of the non-aerated zone was the conversion of slowly biodegradable matter into short chain fatty acids, easily oxidized in the anoxic and aerobic processes. Anyway,

it is possible that the anaerobic COD removal was underestimated because a part of methane was probably stripped in the aerobic zone. The main reason for the low extension of the anaerobic process was the high mixing pattern existing in the integrated reactor, which justified that the in situ measure of dissolved oxygen concentration in the samples taken from the bottom of the anaerobic zone were dissolved oxygen, which seriously limited the anaerobic process. In fact, the biomass accumulated at the bottom of the aerated zone did not present any nitrifying activity, according to the respirometry tests.

Table1: Feed and effluent wastewater characteristics

 

COD

BOD5

NH4+

NTU

pH

Coliforms

E. coli

Influent

450

270

18

95

6-8

4x103

>1600

Effluent

80

30

2.5

<5

7.2

400

<30

Medical wastewater treatment technology by AAO

AAO is a biotechnology that efficiently treats wastewater containing high levels of nutrients such as household wastewater, hospital wastewater, food processing industry, confectionery, aqua ... The stages in the AAO process include: Anaerobic (anaerobic biological sludge) - Anoxic (oxygenated aerobic bioreactor) - Oxic (aerobic biological sludge), then disinfection will be performed by microfiltration as MBR Or chemical disinfectants such as chlorine.

Processing principle according to AAO technology:

  • Anaerobic: to remove hydrocarbons, precipitated heavy metals, phosphorus precipitates, activated chlorine ... In anaerobic tanks, the process is mainly the operation of the anaerobic microorganism. In the process of growth and development, anaerobic microorganisms will absorb dissolved organic substances in waste water, decompose and convert them into gaseous compounds. The resulting gas mixture is often referred to as biogas or biogas.
  • Anoxic: To reduce NO3 to N2 and to further reduce BOD, COD. In wastewater, containing nitrogen and phosphorus compounds, these compounds need to be removed from the wastewater. In the Anoxic tank, in the absence of anaerobic micro-organisms, N and P treatment developed via nitrification and phosphoril. N2 molecular nitrogen gas forms out of water and out. Phosphorus-containing organic compounds will be transformed into new microorganisms that do not contain phosphorus and phosphorus-sensitive compounds but are easily biodegradable for aerobic species.
  • Aerobic (Oxic or Aerobic): to convert NH4 to NO3, reducing BOD, COD, sulfur ... This tank uses aerobic microorganisms to decompose waste. In this tank, microorganisms that are suspended in suspended form (activated sludge) absorb oxygen and organic matter (pollutants) and use nutrients such as nitrogen and phosphorus to synthesize new cells. CO2 emissions, H2O and energy.

Advantages of AAO technology:

  • Highly effective treatment of hospital wastewater (hospital); wastewater after treatment meets the standards of medical wastewater (QCVN 28: 2010/BTNMT).
  • Low operating and management costs.
  • It is possible to relocate the treatment system easily, rearranging or relocating facilities.
  • When expanding the scale, increase the capacity, it is possible to connect the module block without having to dismantle, replace.
  • The closed module should easily create beautiful, not disperse bad smell to the surrounding area.


Collected pits are usually deep in size to collect wastewater. In the collecting pit, submersible pumps are used to pump wastewater into an air-conditioning tank and regulate the air conditioner and regulate the effluent volume in the production process.Medical wastewater (hospital) in the collection system is led to the collection pit. Prior to entering the collection pit, wastewater is passed through a trash can to remove large trash (≥10mm) to avoid clogging of the pipeline and equipment failure during operation.

In the tank, the wastewater is continuously disturbed by the inlet air blower via the gas distribution system and then the waste water is transferred to the AAO Module to begin the biological treatment process.

At the AAO module, the wastewater is first anaerobically treated at the Anaerobic compartment to remove hydrocarbons, precipitate heavy metals, precipitate phosphorus, remove activated chlorine, and then convert to anoxic treatment for NO3 removal. Into N2 and continue to reduce BOD, COD, eventually to aerobic Oxic (aerobic) to convert NH4 to NO3, reducing BOD, COD, sulfur ... and complete the process.

Also in this aerobic compartment, the membrane bio-reactor (MBR) filters the waste water after treatment and pumps it directly to the receiving source. Because the size of the MBR membrane is very small (0.01 ~ 0.2 μm, smaller than the size of many bacteria), the bio-sludge will be retained in the tank, the high microbial density and increased processing efficiency. Clean water is pumped out without sedimentation, filtration and sterilization.

An external air blower provides the active microorganism with the task of blowing out the membranes to limit the clogging of the membrane. The slurry settles down to the bottom of the tank, which is circulated to prevent anoxia to maintain the sludge concentration, and the excess sludge is injected into the sludge reservoir.

Medical wastewater after treatment to comply with QCVN 28:2010/BTNMT standard, column A.

The residual sludge from the bioreactors and solid sludges from the litter process is also directed to the sludge tank. Anaerobic sludge stabilization takes place over a long period of time, which will make the sludge stable, lose its odor and be easy to settle. Then the sludge is taken to buried.

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