After reading this article you will learn about the aquatic plants, animals and viruses which pollute the water with its biological treatment.
Aquatic Plants which Pollute the Water:
The phyla are of primary importance: The water weeds and the algae.
1. Seed-Bearing Plants (Spermophyta):
Two water weeds are usually attached to the littoral or benthos, but some are free floating. Typifying attached plants are Anacharis (Elodea) and Potamogeton: typifying free-floating plants is Lemna, or duckweed. Few aquatic plants propagate by seed; most are perennial and grow from runners, tubers, buds or stem fragments; examples are the sedges or rushes, such as Scrirpus lacustris.
When conditions of light, temperature, and nutrition are favorable, dense growths of water weeds may infect lakes, ponds, reservoirs, canals, and streams. They furnish shelter and food to other aquatic organisms not competing for the same nutrients. Autumnal decay adds much organic matter to the sheltering waters and is responsible for the deep color of swamp waters during spring thaws.
2. Primitive Plants (Thallophyta):
According to the general classification, the thallophytes are represented only by pigmented members, the algae. Molds are placed in a separate category or kingdom along with bacteria and viruses. The algae are of simple structure and at a level of life at which the division into plants and animals is no longer rigid. They pollute the water.
Four families of algae occur widely.
They are distinguished according to color as:
(3) Grass-green and
(4) Golden-or yellow-brown algae.
Classification could be according to mode of reproduction instead.
Aquatic Animals which Pollute the Water:
Animals of importance in the sanitary economy of water are described briefly in the following paragraphs:
1. Vertebrates (Vertebrata):
Fish and amphibians are the most populous. The welfare of game fish is a particular responsibility in connection with the control of algal growths by chemicals, the pollution of natural waters by organic matter, and the discharge of toxic substances such as insecticides and industrial waste products.
2. Mollusks (Mullusca):
The shellfish occur in wide variety as mussels, slugs, snails, limpets, and cockles. Edible bivalves harvested from polluted waters have transmitted intestinal infections and invasions of mussel beds by toxic dinoflagellates, subsequently ingested by them, have made the mussles poisonous. Encroachment of water intakes by mussels quickly reduces intake capacities.
3. Arthorphods (Arthropoda):
Arthropods possess joined legs or leg-like appendages. The crustaceans (Crustacea) and the spiders and mites (Arachnida) include both large and small genera. The larval stages of many insects abound in water. Some forsake the water environment when they emerge as adults; others remain aquatic throughout their lives; yet others are semi aquatic, infesting trickling filters.
There are three aquatic phyla: the annelids (Annelida) or aquatic earthworms, the nematods (Nematoda), and the rotifiers (Rotifera). The eggs of nematodes and flatworms (Platehelminthes) may survive in water and infect fish and, through them, also man and the higher animals.
However, the flatworms themselves are not truly aquatic. With exception of the rotifers, the preferred habitat of the aquatic worms is in bottom deposits. They are important scavengers.
5. Metazoa Other than Worms (Porifera, Polyzoa, and Coelenterata):
Porifera or sponges are agglomerations of animal cells in gelatinous masses. Polyzoa form mosslike or coral-like calcareous or chitinous aggregations that may reach relatively enormous size. The coelenterates, Hydra, for example, generally occur singly but may appear, often quite suddenly, in large number in water reservoirs and on slow sand filtes.
The medusa craspedacusta likewise infests lakes, ponds, and reservoirs on occasion. Saltwater jellyfish, too, may appear in large numbers and become a nuisance on beaches.
A few species of protozoa are pathogenic to man. Normal aquatic representatives are important scavengers and fall into three classes. Some protozoa thrive under aerobic, others under anaerobic, conditions. Still others are facultative aerobes or anaerobes.
Amoeboid protozoa (Amoebina in the class Rhizopoda or Sarcodina). These simplest of all animals are irregular in shape, necked or shelled, single or colonial. They move by sending forth pseudopodia (false feet). Some genera form spherical, resistant cysts.
Flagellated protozoa (Flagellata or Mastigophora). The flagellates possess whiplike or lashlike appendages. They occur singly or in colonies, naked or in cellulosic shells. Some are plantlike and pigmented (Phytomastigophora); others are animal-like and unpigmented (Zoomastigophora).
Ciliated protozoa (Ciliophora or Infusoria). The ciliates have hairlike appendages and occur singly or in colonies, free-swimming or attached. They may reach large numbers in polluted water and, because they are holozoic, they can be important in the destruction of pathogenic as well as normal bacteria and other living organisms.
Aquatic Molds, Bacteria, and Viruses which Pollute the Water:
The number and variety of aquatic molds, bacteria, and viruses are very large. Although all three groups contain organisms pathogenic to man and the higher animals, most of the species are scavengers that recycle essential nutritional elements with the environment.
None contains chlorophyll. However, pigmented bacteria are able to utilize radiant energy for the synthesis of organic matter. Moreover, as said before, there are unpigmented bacteria that can synthesize organic substances through inorganic chemical reactions.
Biological Treatment Processes:
Biological treatment processes have also been proposed for the removal of phosphorus and nitrogen. In biological phosphorous removal technologies, steps have been included in which the waste passes through a series of reactors, where the sequence of environments have been arranged from anaerobic to anoxic to aerobic.
Here an anaerobic environment is defined as one that contains no oxygen, and anoxic environment is that which is devoid of both free oxygen (O2) and combined oxygen (NO3–, SO42- etc.) forms. The purpose of the successive zones is to allow for the development or growth of microorganisms with specific traits. Acinetobacter bacteria have been found to be capable of assimilating phosphorus during their growth.
The biological phosphorus removal process (Fig.9.) starts with waste water moving into basins where anaerobic and anoxic conditions are maintained. In the basin, the facultative decomposer, cause the release of acetate and other fermentation products from soluble organic matter present in the waste water.
The fermentation products are substrates which are favoured by Acinetobactor and other phosphorus storing organisms, and they stimulate the growth of these species in comparison with other micro-organisms in the general population. The anaerobic conditions provide an environment which results in population selection and development of the phosphorus storing species.
Without the oxygen free phase, such organisms are generally present in very small amounts in the activated sludge. When they enter into the aerobic zone, the selected microorganisms efficiently take up the soluble phophorus from the waste water stream. The phosphorus rich sludge is then removed and treated as usual.
Denitrification process can be used for the removal of nitrogen from waste water. In this process, two types of nitrogen reactions occur in series. In the first step, the environment in aerobic (which favours microbial nitrification) and conversion of aqueous ammonium ion into nitrate takes place).
The second step needs anaerobic environment and denitrification takes places in the presence of denitrifying bacteria such as Pseudomonas, Micrococcus and Achromobacter. In the presence of these bacteria sugars and carbohydrates and other organic compounds in the waste water act as electron donors and soluble nitrate is reduced into N2 gas. In addition, NH4+ and NH3 are obtained as byproducts in small amounts in many cases.
In the above reaction [CH2O] acts as electron donor. Waste water biomass can act as the reducing agent for denitrification, but in practice CH3OH is often added as supplement, because it ensure more rapid and complete reaction under reducing conditions.
A combined biological/chemical system for sequential nitrogen and phosphorus removal can also be achieved by recycling the waste stream. For example, in the phosphorus removal system shown in fig. 1, recycling of the effluent from the aerator into the anaerobic basin creates a system which allows for nitrification/denitrification to take place.
However, removal of the two nutrients using these and other biological waste water treatment plants requires very careful design and control of operating conditions.