Dr Jackson Kung'u- Mold Specialist

Helping People Resolve Mold Problems

Contact Us

Dr. Jackson Kung’u (PhD)- Mold Specialist.
Phone: 905-290-9101
Mobile: 437-556-0254

Home | Fungi

Fungi

Microbial Contamination Of Wastewater

Microbial Contamination Of Wastewater And Associated Health Risks

Wastewater consists of water that carries wastes (dissolved or suspended solids) from homes, businesses, and industries and also stormwater discharges. This water is rich in chemical and biological pollutants. Therefore, wastewater effluents, if not properly treated, can cause a number of ecological, economical, and human health problems such as:

  • algal blooms from nutrient enrichment;
  • depletion of dissolved oxygen – sometimes resulting in fish death;
  • destruction of habitats from sedimentation;
  • health risks from drinking water contaminated with pathogens or toxic chemical substances;
  • loss of revenue from closures of shellfish growing areas; and
  • loss of tourism and recreational opportunities as a result of beach closures and restrictions of beneficial uses of water.

Decontamination of wastewater before it’s released into the environment is therefore very important. This article will focus on microbial contamination of wastewater and sludge and associated health risks.

Health Risks Associated With Wastewater And Sewage Sludge

Microbial contamination of wastewater and sludge is monitored to determine the degree of pollution and potential exposure to harmful bacteria, fungi and enteric viruses. Many of the microorganisms found in sewage sludge are potentially pathogenic. These microorganisms include bacteria, fungi, parasites, and viruses.

The most common type of bacteria found in sewage sludge are of enteric origin (i.e., from the intestines) since sewage contains human waste. Also found are members of the genera Streptococcus, Clostridium, Mycobacterium, and Listeria. The presence and concentration of a given pathogenic microorganism depend, however, on the presence of healthy or sick carriers in a population. The sewage sludge can contain as high as 108 to 109 total coliforms, 106 to 107 of fecal coliforms, and 102 to 103 salmonellae bacteria per gram of dry matter. Generally, bacteria can survive in the soil for a few months. Some are partially or completely rendered inactive by extreme temperatures below the freezing point or by summer dry spells. Before using farmland to which sludge has been applied, a waiting period of a full year, or at least one summer is recommended.

Sludge may also contain a number of pathogenic fungi, such as Aspergillus fumigatus, Candida albicans, and Cryptococcus neoformans. Since human infection by these fungi is through direct contact or inhalation spores and hyphal fragments, workers who handle sludge, and especially those who are immunocompromised, are at the greatest risk.

Parasites pose health risks primarily to workers at sites where sludge has been applied. The important parasites are protozoa (e.g., amoebae, Toxoplasma gondii, Giardia lamblia, and Cryptosporidium sp.) and helminthes (such as Ascaris sp., Trichuris sp., and Taenia sp). These parasites are often present in sludge in the form of cysts or eggs. The eggs and cysts are very resistant and can be destroyed only by heat treatment at temperatures of at least 70 °C. The number of egg and cysts in a kilogram of dry matter range from several hundred to several thousand. Such numbers are very high, given that only a few parasites are required to cause infection. If present in the soil after application of sludge on land, eggs or cysts can survive several years.

Viruses may be present in raw sludge at concentrations as high as 1000 virus particles per gram of dry matter. Most of the viruses are those that attack the digestive system, i.e., enteric viruses including the hepatitis A virus. In the soil, some viruses can survive for several months in the first 5-15 cm of soil thus posing a health risk to humans.

Monitoring Microbial Contamination Of Wastewater

filter membrane with colonies

Since it’s not practical to test for every potentially pathogenic organism in wastewater, the degree of pollution of wastewater is determined by use of indicator organisms. Two groups of organisms used as indicators of pollution are the total coliforms and fecal coliforms. The fecal coliform group, however, is considered the most significant by majority of laboratories.

The coliform group of organisms consist of primarily the genera Escherichia, Enterobacter, Citrobacter, and Klebsiella. The coliforms are widely distributed in nature, and many are in the gut of humans and warm-blooded animals.

A more rigorous test to assess the extent of fecal contamination may involve testing a suite of microbial indicators (e.g., total and fecal coliforms, enterococci, Escherichia coli, coliphage, Clostridium perfringens, and human enteric viruses).

Collection Of Samples

Sampling is a critical part of sanitary water testing. As often stated, the laboratory results are only as good as the sample collected. Therefore, it’s not only important that the sample accurately represents the mass of water being tested but also to prevent deterioration and contamination of the sample before analysis.

Generally there are two methods for sampling wastewater. The grab sampling and composite sampling. Grab sampling refers to a sample collected at one time. The disadvantage of a grab sample is that it reflects the condition of the water only at the point in time that the sample was collected. Composite sampling, on the other hand consists of a collection of numerous individual discrete samples (about 100 mL each) taken at regular intervals, usually of 1 hour over a period of 24 hours. The collected samples are poured into a larger bottle and kept refrigerated at around 4 oC over the sampling period. The analysis of this composite sample, collected over a period of time, represent the average condition of the wastewater during the collection period.

counting coliform colonies

Sample containers

Two types of sample containers may be used: a wide-mouth, 120 mL borosilicate glass bottle with glass stopper or screw-cap closure or an autoclavable, nontoxic polypropylene bottle. The containers must be sterilized before use.

Sample Treatment And Handling

If the sample to be tested contains residual chlorine, it has to be dechlorinated. This is achieved by adding appropriate amount of sodium thiosulphate dechlorination agent to the bottle before sample collection. This amount is typically 1.0 mL of 1% solution of sodium thiosulphate for a 120-mL bottle and is typically added before sterilization of the bottle.

Ideally, the sample should be processed within 1 hour of collection or refrigerated below 10 °C and then processed within 6 hours. When collecting samples, sufficient space (approximately 2.5 cm) in the bottle should be left to allow mixing of the sample by shaking. Contaminating the mouth of the bottle with hands or other non-sterile objects should be avoided.

Testing For Total Coliforms And Fecal Coliforms In Wastewater

The two accepted methods used to test for total coliforms and fecal coliforms are the membrane filter procedure and the most probable number (MPN) method. The former is the most commonly used today because it’s easy to use, accurate, inexpensive, and results are obtained within 24 hours.

On M-Endo medium coliform colonies appear golden-green sheen at 10x magnification under a fluorescent light source. The coliform count of the sample size tested is expressed as the number of colony forming units (CFU) per 100 mL of water. Although each colony of organisms recovered on the membrane filter typically represents one organism, occasionally, more than one organism will merge to form a larger than normal colony.

To be considered valid, the number of coliform colonies on the filter surface should not exceed 80 CFUs, and the total number of all colonies should not exceed 200 CFUs. If these limits are exceeded, the sample should be diluted appropriately to give between 20 to 80 coliform colonies and less than 200 of total number of all colonies.

Fecal Coliforms ferment lactose at elevated temperatures as well as at 35 °C. The incubation temperature required is 44.5 plus or minus 0.2 °C. When grown on M-FC medium, they appear as blue colonies. No more than 60 fecal coliforms, or more than 200 of total colonies should be present on the membrane for a valid count.

coliform colonies on filter membrane

Results Interpretation

The recovery of fecal coliform organisms in wastewater is an indication of possible presence of enteric pathogens.

Jackson Kung’u is the Principal Microbiologist, Mold & Bacteria Consulting Laboratories (MBL) Inc.

Mould Growth

Dampness and mould growth are recognised as major problems affecting a
significant proportion of houses in the North America. Apart from health problems associated with dampness and mould growth, wood decay is also significant problem.

Mould growth in houses is unsightly. But most important, there is considerable evidence to support the view that mouldy housing has a detrimental effect on the health of occupants residing in such environments. This is a cause for concern, considering that many individuals spend most of their time indoors especially during winter. Respiratory problems and allergic reactions are the common health problems associated with mould. Generally, indoor moulds affect people through inhalation of airborne spores. High levels of airborne spores may occur due to growth of mould on walls and furnishings.

Requirements For Mould Growth
Requirements for mould growth in buildings include:

  • nutrients: found in the materials which make up or are deposited on indoor surfaces
  • oxygen. Like most other living things, common indoor moulds require air (oxygen) for growth.
  • suitable temperature (around 25 degrees Celcius)
  • moisture: the relative humidity (RH) at a surface is the best indicator of moisture available for mould growth.

In most cases, mould growth in homes is caused by condensation. Condensation in buildings occurs where moist air meets a cold surface. For example if air meets cold water pipes, window glasses or other cold surfaces and is cooled below its dew point temperature, the vapour close to the surface becomes saturated and excess vapour turns to liquid.

There are two types of condensation:

  • Surface condensation. Surface condensation occurs at the surface of the material.
  • Interstitial condensation. Interstitial condensation occurs inside a material. If vapour passes through porous building materials and the dew point temperature occurs within that material then the vapour will condense. Interstitial condensation is responsible for mould growth in building envelopes.

The major factors influencing condensation in buildings include:

  • Moisture production from sources inside the building. Moisture sources include respiration, cooking, washing and drying of clothes.
  • Air and structural temperatures
  • Ventilation. Proper ventilation helps to reduce condensation. 

Diesel from fungi?

A tree fungus, called Gliocladium roseum, has been found to produce a volatile gas similar to diesel. The fungus is able to breakdown cellulose in plant material, under limited oxygen, directly into diesel. The strain producing diesel was discovered by Dr Gary Strobel, a professor at Montana State University. Dr Strobel uses the term “myco-diesel”. Dr Strrobel believes myco-diesel could be an option for those who want alternatives even to ethanol.

For more details visit the Science Daily Website

Wood Rot Fungi

What are wood rot fungi? Wood is one of the major components of building materials in residential and office buildings. In fact it’s almost impossible to miss a wooden item in a building. It is subject to attack by wood rot fungi and other organisms if it’s not well preserved.

Growth Requirements for wood rot fungi

For fungi to colonize wood, the following conditions are required:

  • Favourable temperatures. Generally wood colonizing fungi have optimal growth temperature at aound 25 degrees Celsius.
  • Adequate moisture. Moisture is the most critical requirement for fungi to colonize wood. Fungi will not attack dry wood (i.e., with a moisture content of 19 percent or less). Decay fungi require a wood moisture content of about 30%.
  • Adequate oxygen. Most fungi require (oxygen) for growth.
  • Food source. Like every other living organism, fungi require nutrients for growth. These are readily available on wood surfaces in form of dust. The wood itself is made of biodegradable compounds (cellulose, hemicellulose,lignin).

wood rot fungiThere are 2 groups of wood rot fungi. These are the wood-decaying fungi (wood-rotting fungi) and the Wood-staining fungi (sapstaining fungi).

Wood rot fungi
The wood-decaying fungi are the most damaging of all the wood destroying fungi. These fungi are prolific producers of strong enzymes that they use to breakdown complex wood components (cellulose, hemicellulose,lignin) to simple sugars that they can utilize as food.

Wood-decaying fungi

Wood-decay fungi colonize the sapwood and heartwood of most tree species. These fungi grow inside the wood and/or on wood surfaces. On the wood surface they appear as fan-shaped patches of fine, threadlike, cottony growths or as rootlike shapes. The color of these growths may range from white through light brown, bright yellow, and dark brown. The spore-producing structures (fruiting bodies) of the fungus may take the form of mushrooms, shelflike brackets, or flattened, crustlike structures. Fine, threadlike fungal strands called mycelia grow throughout the wood and excrete enzymes that digest parts of the wood as food. By breaking down the cellulose, hemicellulose,and lignin wood the strength and other properties of the wood are destroyed.

The rate of decay and extent of deterioration depend on the duration of favorable conditions for fungal growth. Decay will stop when the moisture content is lower than the fungu’s requirements. Decay slows down significantly if the temperature of the wood is either too low or too high. Early decay is more easily noted on freshly exposed surfaces of unseasoned wood than on wood that has been exposed and discolored by the weather. Wood decay fungi are generally grouped into three major categories: brown rot, white rot, and soft rot.

Brown Rot

Brown rot fungi such as Poria monticola and Serpula lacrymans break down primarily the cellulose component of wood for food,leaving a brown residue of lignin. Wood severely infested with brown rot fungi is greatly weakened even before decay is visible. Advanced stages of brown rot infestation are characterised by:

  • The dark brown color of the wood
  • Excessive shrinkage
  • Cross-grain cracking
  • The ease with which the dry wood substance can be crushed to a brown powder.

Brown rot fungi are probably the most important cause of decay of softwoods used in aboveground construction in North America. Brown rot-decayed wood, when dry, is sometimes called “dry rot.”

A few fungi such as Serpula lacryman can decay relatively dry wood by using water-conducting strands (rootlike structures called rhizomorphs) that can carry water from damp soil to wood in lumber piles or buildings. These fungi can decay wood that otherwise would be too dry for decay to occur. They are sometimes called the “dry rot fungi” or “waterconducting fungi.”

White Rot

The white rot fungi, Phellinus megaloporus and Poria contigua, break down both lignin and cellulose in wood. They have a bleaching effect that may make the damaged wood appear whiter than normal. Affected wood shows normal shrinkage and usually does not collapse or crack across the grain as with brown rot damage. However, the infested wood loses its strength gradually until it becomes spongy to the touch. White rot fungi usually attack hardwoods, but several species can also cause softwood decay.

Soft Rot

penicillium on woodSoft rot fungi such as Chaetomium globosum usually attack very wet wood, causing a gradual and shallow (3-4 mm) softening from the surface inward that resembles brown rot. The infested wood surface darkens and becomes very soft, hence the name soft rot.

Wood-staining fungi

Unlike the wood-decay fungi, wood-staining fungi are only a cosmetic problem. They tend to grow on the surface of wood. Examples of wood staining fungi include Ceratostomella spp. and Diplodia spp. These fungi penetrate and discolor sapwood, particularly of softwood species. Typical sapstain, unlike staining by mold fungi, cannot be removed by brushing or planing. Sapstain fungi may become established in the sapwood of standing trees, sawlogs, lumber, and timbers soon after they are cut and before they can be adequately dried. The strength of the wood is not greatly affected, but the wood may not be fit for use where appearance is important (such as siding, trim, furniture, and exterior millwork that is to be clear-finished).

Superficial Wood Colonizing Fungi

Superficial wood colonizing fungi such as Fusarium spp and Penicillium spp., first become noticeable as green, yellow, brown, or black, fuzzy or powdery surface growths on the wood surface. The colored spores they produce can usually be brushed, washed, or surfaced off. On openpored hardwoods, however, the surface molds may cause stains too deep to be easily removed. Freshly cut or seasoned wood stockpiled during warm, humid weather may be noticeably discolored with mold in less than a week. Molds do not reduce wood strength, but they can increase the capacity of wood to absorb moisture, thus increasing the potential of attack by decay fungi.

Biodeterioration

Biodeterioration is a terminology used to describe any undesirable change in the properties of a material caused by the vital activities of organisms.

Fungal growth requires suitable temperature, moisture and air (oxygen). Fungi are heterotrophs that acquire nutrients by absorption. They secrete hydrolytic enzymes (exoenzymes) and acids to decompose complex molecules into simpler ones that can be absorbed and used as nutrients. Hence, they are believed to be potential contributors to biodeterioration of different kinds of materials containing cellulose, silicate mineral (mica and orthoclase), iron and magnesium-bearing minerals (biotite, olivine, pyroxene) etc.

Fungi cause biodeterioration to many materials including:

  • building materials
  • animal feeds
  • electrical equipment
  • food including meat, fruits and grains
  • fuel including jet fuel
  • glass and optical equipments
  • gunpowder
  • leather
  • monuments
  • paint
  • paper
  • tobacco etc.

 How are Fungi involved in biodeterioration?

The rate of biodeterioration depend on prevailing environmental conditions and the fungus involved. There are different mechanisms of biodegradation. These include microbial corrosion, hydrocarbon degradation and biodegradation of cellulose.  Aspergillus niger, Chaetomium globosum, Scopulariopsis brevicaulis, Trichoderma koningii, Trichothecium roseum and Eurotium chevalieri are cellulolytic fungi. Their efficiency to degradate cellulosic (cellulose containing) materials is due to their ability to produce large amounts of cellulase enzymes. 

Stachybotrys chartarum is a common fungus growing on paper (such as that covering gypsum wallboard) in damp buildings.

Some fungi cause blue stain and soft rot of wood, discolouration and loss of strength of cotton materials.  Many fungi spoil food in storage. Aspergillus flavus grows on peanuts and many other substrates, producing a mycotoxin called aflatoxin, which contaminate food and causes liver damage. Fusarium graminearum grows on feed corn and produces the  mycotoxin zearalenone that causes oestrogenic syndrome in animals.

Through the action of excreted oxalic and citric acids fungi can deteriorate marble, limestone, granite and basalt. Several species of fungi are involved in biodeterioration of stone monuments in different countries. Some of these fungi are Aspergillus elegans, Aspergillus flavus, Aspergillus nidulans, Aspergillus niger, Aspergillus versicolor, Alternaria sp, Cladosporium cladosporioides, Cladosporium sphaerospermum, Cunninghamella  echinulata, Curvularia lunata, Fusarium roseum,  Gliocladium virens, Penicillium crustosum, Penicillium glabrum, Penicillium chrysogenum (=Penicillium notatum), Rhizopus arrhizus.

Biodeterioration is a problem worldwide. Several control measures have been applied to prevent the biodeterioration. These include use of fungicides, biological control, prevention of biodeterioration by control of environmental conditions, periodic cleaning of dirt, dust and spores, and use of radiation.