Aquatic weeds and their utilization 361The potential of the local environment to have significant impact on the
organisms in the aquatic system must also be evaluated. Of particular concern in
this regard are:
- local and/or migratory animals that may eat the APU plants, damage
APU levees by burrowing, or upset APU hydraulics by either
channelizing or blocking flow, and - local plant diseases or plant-consuming insects.
As an example, water hyacinths could not be used for wastewater treatment
in an area where biological control of water hyacinths has been established.
Wastewater characteristics
Contaminant concentrations in domestic wastewaters should not be toxic to
aquatic plants in properly designed APU's. As the industrial fraction of the
wastewater increases, the chance of contaminants occurring in toxic
concentrations on a regular basis, or as shock loadings, increases. When an
appreciable portion of the wastewater is of industrial origins, small-scale pilot
studies should be conducted to evaluate the toxicity of the wastewater. If
toxicity from shock loadings occurs, mitigating measures such as flow
equalization/storage facilities will be necessary. If the wastewater is consistently
toxic, source control, pretreatment, or processes other than aquatic treatment
will be necessary.
Process reliability, upsets, and recovery
Little is known about the reliability of aquatic systems. The greater influence of
climatic and other environmental factors on aquatic processes should reduce
their reliability in comparison to conventional processes. However, the slower
rate of treatment, reduced reliance on equipment, and greater bacterial diversity
of aquatic processes should improve their reliability, comparatively. Currently
operating aquatic processes have not been as reliable as conventional processes;
but considering how little is known about the design, monitoring, and
management of aquatic processes, significant improvement in reliability should
be achievable.
Causes of aquatic process upsets and the nature, magnitude, and duration of
disruption of treatment have not been studied. Once rational aquatic treatment
design criteria have been established, most process upsets will result from:
- unusual climatic and environmental events insufficiently accounted
for in design, and - improper APU management, such as lack of plant harvesting, etc.