ACTIVATED SLUDGE AS SEEN BY AN ECOLOGIST

Raw class notes, only about half covered in Spring 1996

holozoic protozoa are predators

same community throughout; if there is bulking sludge, it is throughout the process. It will all inhibited by certain additives.

Organisms found in a trickling filter

  • flies
  • insects + worms
  • succession of communities
  • rotifers + nematodes
  • holozoic protozoa different levels,
  • bacteria + fungi + protozoa
  • nuisance flies dead organic solids

    upper layers may be inhibited or killed while lower layers survive

    While both activated sludge and trickling filters have abundant organisms entering, the process conditions tend not to favor them; these organisms either die out or contribute little to the treatment process and are ignored in most analyses. Some do hang on at low level, and a few may thrive.

    In activated sludge

  • slime formers + filamentous organisms intermixed
  • Zooglea ramigera - gram - , non sporulating, motile, capsulated rods
  • some organisms dead or cannot reproduce
  • if homogenizer used, counts rise 10 to 100 x , 2.2 x 106/ml
  • filamentous organisms usually predominant in bulking sludge
  • Sphaerotilus natans - over 14 strains found
  • fungi uncommon, often have protozoa - good indicators
  • rotifers + nematodes can be significant but often absent
  • phage seldom noted, too much trouble to look
  • how come diversity is maintained? population dynamics + parisitism or predation control
  • prey can hide from predator in slime
  • very few algae because no light
  • floc properties depend on feed - pentoses = dense floc while hexoses = filamentous floc

    inadequate aeration = Sphaerotilus but some disagreement
    microbes are between "declining growth" + endogenous phase
    fungi may dominate for industrial wastes - low O2 because of high BOD

    low N favors fungi, need less/unit mass
    predatory fungus Zoophagus insidiens eats rotifers + lets their prey, bacteria, grow, get poorer nitrification

    Trickling filters (bacteria beds in U.K.)

  • very diverse, shifts to suit waste
  • do not operate as close to starvation conditions as in act sludge, more fungi
  • surface layers have changing predominance with season
  • algae of secondary importance metabolically but luxuriant growth may clog system
  • protozoa very abundant, very different in different strata

    Dosage affects film thickness

    Film changes with season


    Psychoda flies a nuisance but larvae active in metabolism of wastes
    filter is warmer than surroundings, thus active all year
    high BOD has fewer species, maybe less O2
    toxic wastes have fewer species, resistant flies can be very numerous
    size of support medium can direct species, also surface properties
    film properties and presence of a given species are a mutual interaction,

  • i.e., thick film may be unsuitable but organism may produce a thin film
    species distribution varies greatly with depth -
  • at extreme, no active algae in lower depths

    dosing, nozzle design, geometry also affect species selection

    Streams

    Cairns, V.P.I. Used EEG of fish, rate of gill movement to determine effect of industrial wastes. Other effects: sediments, cover benthos, shift fish species away from bottom grazers or cover spawning grounds, may cover stones and disfavor stone-loving fauna

    Trick filt use recirculation to dilute inflow, also to maintain flow and keep floc wet if inflow drops off

  • higher flow bad for flies
  • get ponding in winter - can shift populations
  • slowing rotation rate of arms greatly lowered flies, some worms increased because not eaten by fly larvae
  • fly larvae drop into endogenous growth 2/3 of time if dosed less frequently
  • large, less frequent dose penetrates more, less food for flies
  • may change dosing rate with season, trying to control film by nutrition
  • during start up, get bacterial film readily; protozoa not common in feed thus it takes a while to achieve climax community
  • usually build up feed slowly to establish film and achieve treatment
  • efficiency low until grazing population established
  • don't get nitrification until carbonaceous wastes well removedoften observe an increasing efficiency for new filter, then a serious decline, finally a rise to final condition
  • new bed next to old bed starts fast, inoc. by flies
  • good idea to add humus from old bed

    Idle filters

  • grazers retreat as water drains
  • flies mature, leave in hordes
  • all motile forms, worms, etc. leave with last draining
  • sometimes get fantastic invasion of spiders
  • starts up again much faster than new filter
  • fly control insecticides may give toxic effluent, spray a little at a time

    Brock, T.D. Principles of Microbial Ecology, Prentice Hall 1966 colonies are discrete on a soil particle, adsorption very important:
    no growth in very dilute media, add solid, good growth on adsorbed material
    analogy to calf - 1 month old has high bacteria count, low cellulose digestibility 2 mo., some protozoa, same total bact, good digestibility