Effect of sewage sampling frequency on determination of design parameters for municipal wastewater treatment plants.

The uncertainty associated with the determination of load parameters, which is a key step in the design of wastewater treatment plants (WWTPs), was investigated on the basis of data sets from 58 WWTPs. A further analysed aspect was the organic load variations associated with variable sewage temperatures. Data from 26 WWTPs with a high inflow sampling frequency was used to simulate scenarios to investigate the effect of lower sampling frequencies through a Monte Carlo approach. The calculation of 85-percentile values for chemical oxygen demand (COD) loadings based on only 26 samples per year is associated with a variability of up to ±18%. Approximately 90 samples per year will be necessary to reduce this uncertainty for estimation of COD loadings below 10%. Hence, a low sampling frequency can potentially lead to under- or overestimation of design parameters. Through an analogous approach, it was possible to identify uncertainties of ±11% in COD loading when weekly average data was used with four samples per week. Finally, a tendency to lower COD input loads with increasing temperatures was identified, with a reduction of about 1% of the average loading per degree Celsius.

Energetic flexibility on wastewater treatment plants.

In the future, an additional potential of control reserve as well as storage capacities will be required to compensate fluctuating renewable energy availability. The operation of energy systems will change and flexibility in energy generation and consumption will rise to a valuable asset. Wastewater treatment plants (WWTPs) are capable of providing the flexibility needed, not only with their energy generators but also in terms of their energy consuming aggregates on the plant. To meet challenges of the future in regard to energy purchase and to participate in and contribute to such a volatile energy market, WWTPs have to reveal their energetic potential as a flexible service provider. Based on the evaluated literature and a detailed analysis of aggregates on a pilot WWTP an aggregate management has been developed to shift loads and provide a procedure to identify usable aggregates, characteristic values and control parameters to ensure effluent quality. The results show that WWTPs have a significant potential to provide energetic flexibility. Even for vulnerable components such as aeration systems, load-shifting is possible with appropriate control parameters and reasonable time slots without endangering system functionality.

Generation of diurnal variation for influent data for dynamic simulation.

When using dynamic simulation for fine tuning of the design of activated sludge (AS) plants diurnal variations of influent data are required. For this application usually only data from the design process and no measured data are available. In this paper a simple method to generate diurnal variations of wastewater flow and concentrations is described. The aim is to generate realistic influent data in terms of flow, concentrations and TKN/COD ratios and not to predict the influent of the AS plant in detail. The work has been prepared within the framework of HSG-Sim (Hochschulgruppe Simulation, http://www.hsgsim.org), a group of researchers from Germany, Austria, Luxembourg, Poland, the Netherlands and Switzerland.

Renewable energy for the aeration of wastewater ponds.

The application of a decentralised renewable energy supply for the aeration of wastewater ponds, and the influence of an unsteady oxygen supply on the specific conversion rate and biocoenose was investigated. With the discontinuous aeration the specific conversion rate is increased as compared to facultative ponds. The estimation of the microorganisms consortia was done with in situ hybridisation techniques. A significant shift in the bacteria population with the chosen specific probes for anaerobic, sulphate reducing and nitrifying bacteria could not be detected. Wastewater ponds have sufficient buffer volume to compensate for the fluctuating energy supply. But the efficiency of the energy supply of a photovoltaic plant decreases in shallow lakes (d < 1.5 m) corresponding to a high oxygen production of algae. For the layout of the individual components: photovoltaic and wind power plant, energy management, aeration system and wastewater pond, a simulation model was developed and tested. The application of renewable energy for the aeration of wastewater ponds is a useful alternative for the redevelopment of overloaded ponds as well as the construction of new wastewater ponds, especially in areas with an inadequate central electricity grid and a high availability of wind and solar energy.

Factors influencing whether or not couples seek genetic counselling: an explorative study in a paediatric surgical unit.

To investigate the factors influencing whether or not couples seek genetic counselling, the parents of 37 children with a major congenital anomaly were interviewed at home. All the children had been admitted to the Intensive Care Unit (ICU) of the Department of Paediatric Surgery. After physical examination of the child, the consultant clinical geneticist stated that genetic counselling was indicated for the parents. Whether they sought genetic counselling was left to the parents to decide. Eighteen of the 37 parents had sought genetic counselling. Assessment of the joint influence of a number of factors revealed that two factors were separately paramount in distinguishing between couples who did seek genetic counselling and those who did not: whether parents considered genetic counselling useful in their case shortly after the birth of their affected child, and whether the couple was clearly and correctly informed about the indication for genetic counselling. The intention to have a subsequent pregnancy was not associated with whether or not couples sought genetic counselling. Loss of information was observed: 1/3 of the referrals for genetic counselling mentioned on the written consultation forms were not stated in the discharge letters. This loss of information could have been reduced by a) routinely including the indication for genetic counselling in the discharge letter and b) appointing a coordinating physician to ensure that the parents were informed clearly about the availability of genetic counselling. Resistance to genetic counselling needs to be respected by the physician. Exploring its background might help to reduce this resistance.