J. Krampe

Phosphorus recovery from municipal wastewater: An integrated comparative technological, environmental and economic assessment of P recovery technologies

Phosphorus (P) is an essential and limited resource. Municipal wastewater is a promising source of P via reuse and could be used to replace P derived from phosphate rocks. The agricultural use of sewage sludge is restricted by legislation or is not practiced in several European countries due to environmental risks posed by organic micropollutants and pathogens. Several technologies have been developed in recent years to recover wastewater P. However, these technologies target different P-containing flows in wastewater treatment plants (effluent, digester supernatant, sewage sludge, and sewage sludge ash), use diverse engineering approaches and differ greatly with respect to P recycling rate, potential of removing or destroying pollutants, product quality, environmental impact and cost. This work compares 19 relevant P recovery technologies by considering their relationships with existing wastewater and sludge treatment systems. A combination of different methods, such as material flow analysis, damage units, reference soil method, annuity method, integrated cost calculation and a literature study on solubility, fertilizing effects and handling of recovered materials, is used to evaluate the different technologies with respect to technical, ecological and economic aspects. With regard to the manifold origins of data an uncertainty concept considering validity of data sources is applied. This analysis revealed that recovery from flows with dissolved P produces clean and plant-available materials. These techniques may even be beneficial from economic and technical perspectives under specific circumstances. However, the recovery rates (a maximum of 25%) relative to the wastewater treatment plant influent are relatively low. The approaches that recover P from sewage sludge apply complex technologies and generally achieve effective removal of heavy metals at moderate recovery rates (~40-50% relative to the WWTP input) and comparatively high costs. Sewage sludge ash is the most promising P source, with recovery rates of 60-90% relative to the wastewater P. The costs highly depend on the purity requirements of the recycled products but can be kept comparatively low, especially if synergies with existing industrial processes are exploited.

Phosphorus recovery from digested sewage sludge as MAP by the help of metal ion separation

This study was designed to solve metal ion influence problem on phosphorus recovery from digested sewage sludge as MAP. The experimental steps were proceeded to maximize MAP production and its quality. Used experimental steps were: All digested sewage sludge samples were taken from Stuttgart University sewage treatment plant for research and education (LFKW). Four different forms of LFKW digested sewage sludge were used as feeding sample. These were: original digested sludge, diluted digested sludge, centrifuged digested sludge and incinerated digested sludge. A Donnan membrane unit having a Nafion 117 (DuPont) cation exchange membrane was used to remove metal ions from the samples used. Highest metal ion removal efficiencies, which were 98%, 97%, and 80% for Al, Ca and Fe ions, respectively, were obtained from incinerated digested sludge run. Incinerated digested sludge run was used as preliminary step for MAP production and high quality MAP was produced. Produced MAP fulfils all requirements related with Düngemittelverordnung 2003 and it could be used as a fertilizer in Germany.

Energy benchmarking of South Australian WWTPs.

Optimising the energy consumption and energy generation of wastewater treatment plants (WWTPs) is a topic with increasing importance for water utilities in times of rising energy costs and pressures to reduce greenhouse gas (GHG) emissions. Assessing the energy efficiency and energy optimisation of a WWTP are difficult tasks as most plants vary greatly in size, process layout and other influencing factors. To overcome these limits it is necessary to compare energy efficiency with a statistically relevant base to identify shortfalls and optimisation potential. Such energy benchmarks have been successfully developed and used in central Europe over the last two decades. This paper demonstrates how the latest available energy benchmarks from Germany have been applied to 24 WWTPs in South Australia. It shows how energy benchmarking can be used to identify shortfalls in current performance, prioritise detailed energy assessments and help inform decisions on capital investment.

Practical application of wastewater reuse in tourist resorts

A medium-scale membrane bioreactor was tested in a large tourist resort on the south-western coast of Turkey with the treated wastewater subsequently being used for irrigational purposes. The wastewater treatment system was designed to eliminate carbonaceous and nitrogenous substances. Treatment efficiency was monitored by means of regular chemical and microbiological analyses. Information was collected on water use at different locations of the hotel. Specific values based on the number of guests were determined. Wastewater streams from kitchen, laundry and rooms were analysed to investigate the various contribution from these points. The social acceptance of the guests concerning the on-site wastewater treatment and reuse in the hotel was analysed using a questionnaire. The investigations indicated that the treated wastewater provides the required chemical and hygienic conditions to satisfy requirement for its reuse in irrigation. The acceptance by guests was encouraging for such applications.

Cycle-time determination and process control of sequencing batch membrane bioreactors.

In this paper a method to determine the cycle time for sequencing batch membrane bioreactors (SBMBRs) is introduced. One of the advantages of SBMBRs is the simplicity of adapting them to varying wastewater composition. The benefit of this flexibility can only be fully utilised if the cycle times are optimised for the specific inlet load conditions. This requires either proactive and ongoing operator adjustment or active predictive instrument-based control. Determination of the cycle times for conventional sequencing batch reactor (SBR) plants is usually based on experience. Due to the higher mixed liquor suspended solids concentrations in SBMBRs and the limited experience with their application, a new approach to calculate the cycle time had to be developed. Based on results from a semi-technical pilot plant, the paper presents an approach for calculating the cycle time in relation to the influent concentration according to the Activated Sludge Model No. 1 and the German HSG (Hochschulgruppe) Approach. The approach presented in this paper considers the increased solid contents in the reactor and the resultant shortened reaction times. This allows for an exact calculation of the nitrification and denitrification cycles with a tolerance of only a few minutes. Ultimately the same approach can be used for a predictive control strategy and for conventional SBR plants.

The influence of temperature and SRT on high-solid digestion of municipal sewage sludge

The influence of temperature and solids retention time (SRT) on high-solid digestion of municipal sewage sludge was investigated in laboratory-scale reactors. Digestion with high-solid concentration reduces the required digestion volume and is advantageous for urban areas. The experimental conditions comprised total suspended solids (TSS) in digested sludge between 4.0 and 4.6%, temperatures in a range of 33 to 41 °C and the SRT between 10 and 25 d. High-solid digestion operates with increased NH4-N concentrations released from organic compounds. The anaerobic process can be limited by high NH4-N concentration and toxic NH3. In this study a stable digestion was observed up to 2,000 mg L(-1) NH4-N and 75 mg L(-1) NH3. Volatile suspended solids (VSS) and chemical oxygen demand removal was 53% and 57% respectively. However, digestion with 10 d SRT led to a declined VSS removal of 49%. The removal at 41 and 37 °C showed minor differences, while reduced NH4-N release and reduced methane production were observed at 33 °C. For economic reasons, high-solid digestion at 41 °C is not recommended, but will not impair VSS removal. The outcomes of this study confirm that digestion with up to 7.8% TSS in the feed is feasible for the tested temperatures and SRT down to 15 d.

Crucial elements and technical implementation of intelligent monitoring networks

Growing complexity of water monitoring instrumentation leads to specialized solutions in respect to sensor integration across several measurement device suppliers. Despite efforts of standardization for data interfaces and protocols, problems regarding the combination of several devices to gain the complete picture in terms of water quality remain. This assessment, especially accomplished from the perspective of a catchment area, requires a transition from sole use of data collectors toward an implementation of intelligent measurement networks. Several challenges and bottlenecks concerning distributed data collection are discussed starting with data acquisition up to the user-scope of utilizing data processing software. Finally, experiences using automated data inspection and export tools are discussed and a brief overview of expectable long-term data availability is given.

Effect of pH control strategies and substrate concentration on the hydrogen yield from fermentative hydrogen production in large laboratory-scale.

A series of batch experiments investigating two different pH control strategies, initial pH adjustment and continuous pH control, have been carried out in large laboratory-scale reactors with working volumes of 30 L. In both cases, pH was varied between 5 and 7.5. Sucrose concentrations were also varied starting from 0 up to 30 g/L. Higher hydrogen production yields can be achieved by batch experiments through continuous pH control than by simple initial pH adjustment. In the case of continuous pH control, maximization of hydrogen yield was acquired for slightly acidic pH of 6.5. Continuous pH control in the neutral pH range of 7.0 and in pH lower than 6.5, induced a reduction in the hydrogen production yield. Sucrose can be completely degraded only for a pH higher than 6. Lower pH values seem to inhibit the hydrogen-producing bacteria. Under the conditions of continuous pH adjustment at pH 6.5 and a sucrose concentration of 25 g/L the maximum hydrogen yield of 1.79 mol H(2)/mol hexose was obtained. These conditions could be applied for the batch start-up of large fermentors.

Energy consumption of agitators in activated sludge tanks – actual state and optimization potential

Depending on design capacity, agitators consume about 5 to 20% of the total energy consumption of a wastewater treatment plant. Based on inhabitant-specific energy consumption (kWh PE120-1 a-1; PE120 is population equivalent, assuming 120 g chemical oxygen demand per PE per day), power density (W m-3) and volume-specific energy consumption (Wh m-3 d-1) as evaluation indicators, this paper provides a sound contribution to understanding energy consumption and energy optimization potentials of agitators. Basically, there are two ways to optimize agitator operation: the reduction of the power density and the reduction of the daily operating time. Energy saving options range from continuous mixing with low power densities of 1 W m-3 to mixing by means of short, intense energy pulses (impulse aeration, impulse stirring). However, the following correlation applies: the shorter the duration of energy input, the higher the power density on the respective volume-specific energy consumption isoline. Under favourable conditions with respect to tank volume, tank geometry, aeration and agitator position, mixing energy can be reduced to 24 Wh m-3 d-1 and below. Additionally, it could be verified that power density of agitators stands in inverse relation to tank volume.

Optimization of ozonation and peroxone process for simultaneous control of micropollutants and bromate in wastewater

The study aims to simultaneously control micropollutants and bromate formations by using ozonation and peroxone process. The batch experiments were run with variations in specific ozone dose (SOD) and hydrogen peroxide-to-ozone (H2O2/O3) ratio. Based on the removal by ozonation and peroxone, micropollutants were categorized into three groups: non-reactive compounds (i.e. amidotrizoate), moderately reactive compounds (i.e. metoprolol, acesulfame potassium, bezafibrate, and benzotriazole), and highly reactive compounds (i.e. carbamazepine and diclofenac). For ozonation and peroxone process, the removals for highly reactive compounds and moderately reactive compounds were 82-99% and 29-99%, respectively. The removal of amidotrizoate was not observed in this study. The effect of ozonation on micropollutant removals was similar to the peroxone process. However, differences in bromate formation were observed. Bromate formation depended on the SOD, while addition of hydrogen peroxide suppressed the bromate formation. The peroxone process at the H2O2/O3 ratio of 0.3 was recommended to bromide-containing water below 100 µg·L-1 for simultaneous control of micropollutants and bromate. Enhancement in micropollutant removals, except for the non-reactive groups, was achieved with either higher SOD or the addition of hydrogen peroxide to ozonation. The micropollutant removal predicted from the second-order kinetic reaction with ozone and •OH exposures was higher than the observed data.