Lecturer: Dr. Hul Seingheng By: Group 5 (I3 GCA)

Students : MAO Chanthy MEAS Sophea MENG Sophang MORM Elen OENG Seikleng

Fixed film processes

Raw wastewaters which were overcharged with organic and nitrogen pollution have long been discharged directly to receiving water.

These substances can cause in a chronic state of degradation. So wastewater treatment is needed.

1. Introduction

One of the most popular types of treatment is the biological one.

There are main families of wastewater treatment process:

a. the fixed film processes,b. the suspended growth processes.

1. Introduction

2.1 Biofilm development The biofilm formation process1. Bacterial adhesion2. Adsorbed microorganisms grow, reproduce

and produce extracellular polymeric substances, which frequently extend from the cell forming a gelatinous matrix called a biofilm.

After some microorganisms have adhered to a surface medium, they start growing producing the biofilm, which is aerobic.

2. Fixed film processes in wastewater treatment

A general one for all types of fixed film processes found in wastewater treatment is difficult to establish as many factors can be considered:

+ type of medium+ type of reactor + environmental conditions +wastewater characteristics+types of pollutants to be removed

(C,N,P, xenobiotics )

2.2 Usual processes

The trickling filter which is very efficient with respect to adhesion of bacteria was the first fixed film process that was developed.

It is a packed bed reactor (2-3m deep) filled with a medium consisting of 5-10cm stones with a specific surface area of 40-100m2/m3.

It will be classified as low, standard ( or intermediate) and high rate depend mainly on the organic and hydraulic loading rate.

2.2.1 Trickling filters

Rotating biological contactor (RBCs) consist of a series of circular plastic disk mounted on a horizontal central shaft and distanced at 1.5-2.5cm

Normally 40% of the disks surface is submerged and they are rotated in a tank containing the wastewater.

Attached microorganisms rotate into the water, where organic matter is adsorbed onto the biofilm, and out of the wastewater, where the oxygen necessary for the conversion of organic matter is obtained by adsorption from the air.

2.2.2 Rotating biological contactor

There are two main types of biological aerated biofilters:

a. down flow biofilters b. up flow biofilters

2.2.3 Biological aerated biofilters

b. up flow biofilter

For all processes, the continuous addition of substrate and microorganisms present in the wastewater encourage the formation of a complex biofilm composed of bacteria, fungi, protozoa, macro invertebrates (larvae, worms) and sometimes algae.

2.3. Microbiology of standard processes

Bacteria are unicellular prokaryotic organisms. They are the first to colonize the biofilm for the fixed film treatment processes.

These genera are found in the biofilm are: Heterotrophic rod-shape organisms:

Zooglea, Pseudomonas, Chromobacter, Achromobacter, Alcaligenes and Flavobacteria.

2.3.1. Bacteria

Filamentous bacteria: Beggiation, Thiotrix and Spaerotilus. They are nitrifying organism like Nitrosomonas and Nitrobacteria.

Role: They take part in the removal of the soluble pollutant matter. But E. coli or Nocardia spp. perform less well than others in removal carbonaceous pollution.

2.3.1. Bacteria

Fungi are the single or multi-cellular eukaryotic organisms.

The most frequent fungi colonizing fixed film processes are: Sepedonium spp., Subarromyces slendens, Ascoidea rubescens, Fusarium aquaeductuum, Geotrichum candidum and Trichosporon cutaneum.

2.3.2 Fungi

Role: They are important for purifier, especially for the carbonaceous substrate.

However, the conversion rate is much higher than for bacteria and it encourages a significant production of biomass for a give quantity of substrate.

Especially, it seems fungi have very specific growth cycles based on the season.

Winter and early spring: there are maximum number of fungi growth

Midsummer: They become rare

2.3.2 Fungi

Protozoa are unicellular eukaryotic organisms widespread in fixed film processes.

They are divided into three branches:-Mastigophora: phytomastigina and

zoomastigina-Rhizopoda: heliozoan and amoebae-Ciliophora: ciliated

They mainly feed on organic particulate matter, bacteria, algae or other protozoa.

2.3.3. Protozoa

Several photosynthetic organisms, algae and cyanobacteria can growth exposed to light at the surface of biofilm.

Algea: single or multicellulaire photosynthetic eukaryotes.

Cynobacteria (blue-green): unicellular photosynthetic prokaryotes.

2.3.4 Algea and cyanobacteria

The frequently found genera include: Ulothrix, Phormidium, Anacystis, Euglena, Stigeolonium, Chlorella and Oscillatoria.

Role: Algea and cynobacteria only play a small role in fixed film processes. Some species like Phormidium cyanobacterium, develop into multilayers at the surface of the trickling filter and decrease the efficiency of the process.

2.3.4 Algea and cyanobacteria

Cyanobacteria

Algae

Metazoa are multicellulaire eukaryotic organisms that encompass the phyla of worms (rotifers, nematodes, gastrotricha and oligochaetes) and arthropods (arachnids, tardigrades, crustaacea, myriapod and insects).

These predators and detrivivorous organisms feed on the biofilm, embrittle it, encourage loosening, decrease biomass volume and accelerate mineralization.

2.3.5 Metazoa

Their grazing capacity also helps avoid clogging of trickling filters through biofilm consumption.

2.3.5 Metazoa

Some microorganism species, favoring or not proper processes operation, will develop with relation to various operational parameter such as: substrate, nutrients, dissolved oxygen, temperature, pH, and hydraulic loading.

2.3.6 Environmental effects on biofilm ecology

2.4 Comparison between attached and suspended growth

It is important at this stage to make a comparison between suspended and attached growth process before discussion hybrid systems.

The difference between the two type of process : fixed film process seem to be less effect than suspended growth process.

Hybrid system can be defined by two types of process :

-a biofilm reactor (usually a trickling filter)

-a biomass support system

2.5 Hybrid system

2.5.1. System in series Secondary treatment process combining

fixed growth and suspended growth system in series are popular, these process offer simplicity of operation and process stability of fixed film process with the high quality effluent associated with suspended growth process.

2.5 Hybrid system

Biomass support systems consist of immersing various types of support media in an activated sludge reactor to favor the growth of fixed bacteria.

The support can be fixed in the reactor or can consist of mobile media such as foam pads, small carriers, etc.

2.5.2 Biomass support systems

The main advantages of these systems are improved nitrification and an increase in sludge settleability.

One point that must always be remembered when considering an activated sludge process with biomass supports is that, because of a higher biomass concentration, the volumetric oxygen requirement will be greater in these systems than in conventional activated sludge.

2.5.2 Biomass support systems

Growth of biofilms is a natural process that has been engineered in many ways to treat wastewater.

Fixed film process, developed mainly for the treatment of municipal wastewaters, have been presented here along with their microbiology.

3. Conclusion and Perspectives

Fluidized bed reactors (FBR) are a more sophisticated version of the immersed mobile biomass system presented earlier. Their main advantages are:

-High removal efficiency of C and Ni through large amounts of fixed biomass with a low hydraulic rentention time

-No clogging-Better oxygen transfer-Reduce sludge production.

3. Conclusion and Perspectives

Finally, the development of intensive processes may be of interest, but there is a growing need for the development of extensive processes (low cost and low operational requirements) for on site and small community wastewater treatment.

3. Conclusion and Perspectives

Thanks for your listening my presentation.

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