Peter Cornel

Phosphorus recovery from wastewater: needs, technologies and costs

Phosphorus is an essential, yet limited resource, which cannot be replaced by any other element. This is why there are increasing efforts to recycle phosphorus contained in wastewater. It involves the recovery of phosphorus and, normally, the separation of phosphates from harmful substances. Phosphorus can be recovered from wastewater, sewage sludge, as well as from the ash of incinerated sewage sludge, and can be combined with phosphorus removal in most cases. The phosphorus recovery rate from the liquid phase can reach 40 to 50% at the most, while recovery rates from sewage sludge and sewage sludge ash can reach up to 90%. There are various methods which can be applied for phosphorus recovery. Up to now, there is limited experience in industrial-scale implementation. The costs for recovered phosphate exceed the costs for phosphate from rock phosphate by several times. For German conditions, the specific additional costs of wastewater treatment by integrating phosphorus recovery can be estimated at euro2-6 per capita and year.

On wet chemical phosphorus recovery from sewage sludge ash by acidic or alkaline leaching and an optimized combination of both

The advantages and drawbacks of existing wet chemical phosphorus (P) recovery technologies, their applicability to different types of sewage sludge ash (SSA) and the role of the decay products of detergent zeolites as a source of reactive Al in SSA are analyzed. Since neither a purely acidic nor a purely alkaline treatment are able to provide satisfactory technical solutions a wet chemical phosphorus (P) recovery process for sewage sludge ashes (SSAs) is investigated in detail that is based on a sequential treatment of SSA with an acid and a base. As a result of an acidic pre-treatment, the P fraction of the raw SSA that was bound as - alkaline-insoluble - calcium phosphate (Ca-P) is converted into aluminum phosphate (Al-P). This newly formed Al-P can be easily dissolved via alkaline treatment and then easily separated from the alkaline leachate via precipitation of Ca-P. The Al-component can be reused as precipitant for P-removal in waste water treatment plants (WWTPs). The investigated process requires fewer chemicals than the direct acidic dissolution of all P-compounds contained in the SSA. This is due to the described rearrangement of the P component from Ca-P to Al-P. That such a rearrangement of P occurs indeed was confirmed through a combination of XRD, ICP and XRF analyses together with mass balance calculations. The present investigation proves that the process works for very different types of SSAs: For Al-rich SSAs that come from WWTPs where Al-salt is used for chemical P-removal the described sequential treatment process works best and yields P-recovery rates as high as 70-77%. But even for SSAs from WWTPs where only iron salt is used for chemical P-removal, a considerable amount of the reactive Al necessary for the described P-rearrangement is supplied by decay products of detergent zeolites, a hidden Al-source present in most SSAs produced in Europe.

Water-Energy Interactions in Water Reuse

The focus of Water-Energy Interactions of Water Reuse is to collect original contributions and some relevant publications from recent conference proceedings in order to provide state-of-art information on the use of energy in wastewater treatment and reuse systems. Special focus is given to innovative technologies, such as membrane bioreactors, high pressure membrane filtration systems, and novel water reuse processes. A comparison of energy consumption in water reuse systems and desalination will be also provided. Water-Energy Interactions of Water Reuse covers the use of energy in conventional and advanced wastewater treatment for various water reuse applications, including carbon footprint, energy efficiency, energy self-sufficient facilities and novel technologies, such as microbial fuel cells and biogas valorisation. It is of real value to water utility managers; policy makers for water and wastewater treatment; water resources planners, and researchers and students in environmental engineering and science. ISBN: 9781843395416 (Print) ISBN: 9781780400662 (eBook)

Semicentralised supply and treatment systems: integrated infrastructure solutions for fast growing urban areas

Currently, the development of the world population is characterised by two trends: absolute population growth and rapid urbanisation. Especially rapid urbanisation, taking place in Asia, Latin America and Africa, poses major pressure on the affected regions. The development of e.g. Asian countries today is stamped by a combination of urbanisation with high economic growth rates. Conventional centralised infrastructure of supply, treatment and disposal of water is not able to cope with the new challenges arising from these, in history incomparable, high growth rates. Therefore new approaches to infrastructure supply and treatment systems are required - for ecological, sociocultural and economic reasons. The semicentralised approach, focusing on integrated water supply and treatment structures for wastewater and waste on the neighbourhood level, offers one possible solution to the challenges imposed by rapid urbanisation and growing resource needs. The change from centralised to semicentralised supply and treatment systems will minimise the grave discrepancy between the rapid urban growth and the provision of supply and treatment infrastructure. Integrated semicentralised supply and treatment systems face the challenge of growing amounts of wastewater and solid waste combined with rising needs of water for private households and industrial use. The semicentralised approach offers a wide range of flexibility in implementation, energy self-sufficient operation, enormous saving potentials in water demands through intra-urban water reuse and further more advantages in comparison to centralised sectored solutions as practised today.

Wastewater as a Source of Energy, Nutrients, and Service Water

With improving analytical techniques, it becomes more and more obvious that municipal wastewater represents a multisubstance mixture containing probably several hundreds of different substances. However, wastewater consists of H2O to more than 99.5%, a purity which many purchasable products will never reach. This means that potentially valuable substances are present in extreme dilution, in concentrations of mg l−1 down to ng l−1, and mixed with all sorts of other substances. The chapter follows these aspects and faces the ambivalent questions: (1) What prerequisite the wastewater has to fulfill to become a resource? (2) Under which conditions wastewater gets a valuable substance instead of a pollutant?

Free water content and sludge retention time: impact on oxygen transfer in activated sludge.

To investigate the effect of sludge retention time (SRT) and the concentration of mixed liquid volatile suspended solids (MLVSS) on oxygen transfer in activated sludge, we studied mass transfer coefficients (k(L)a) in a pilot-scale membrane bioreactor, which treated synthetic greywater. Additionally, experiments with iron hydroxide flocs were performed to examine the role of free water content in oxygen transfer. The results demonstrate that the alpha-factor is reduced when free water content decreases and floc volume increases. Because the MLVSS concentration in activated sludge mainly regulates floc volume, a reduction of oxygen transfer with increasing MLVSS concentration was observed. If the floc volume remains unchanged, oxygen transfer increases with increasing SRT.

Potentials of using nanofiltration to recover phosphorus from sewage sludge

Due to the depletion of mineral phosphorus resources there is an increasing demand for efficient phosphorus recovery technologies. In this study the potential of nanofiltration to recover phosphorus from pre-treated sewage sludge is investigated. The efficiency of three commercial nanofiltration membranes (Desal 5DK, NP030; MPF34) was tested using model solutions. Desal 5DK showed the best selectivity for phosphorus. A pH of lower than 1.5 was found to be most suitable. Desal 5DK was used on four different sewage sludge ash eluates and on one sewage sludge. In these experiments it was shown that a separation of phosphorus from undesired components such as heavy metals was possible with significant variations in the efficiency for the different ash and sludge types. Additionally the achievable product recovery was investigated with model solutions. A product recovery of 57.1% was attained for pH 1 and 41.4% for pH 1.5.

Prevention of Struvite Scaling in Digesters combined with Phosphorus Removal and Recovery – The FIX-Phos Process

The fixation of phosphorus (FIX-Phos) combines struvite prevention and phosphorus recovery by the addition of calciumsilicatehydrate (CSH) particles into the anaerobic digester. The CSH fixates phosphorus as calcium phosphate and reduces the phosphorus concentration in the sludge water that allows for control of struvite formation. The phosphorus-containing recovery product can be separated and recovered from the digested sludge. In pilot plant experiments, 21% to 31% of phosphorus contained in digested sludge could be recovered when CSH was added at concentrations of 2 g/L to 3.5 g/L to a mixture of primary sludge and waste activated sludge (WAS) from enhanced biological phosphorus removal. The recovery product contained few heavy metals and a phosphorus content of 18 wt % P2O5, which allows for recycling as fertilizer. The fixation of phosphorus within the digester may increase wastewater sludge dewaterability. The phosphorus recycle stream to the headworks of the wastewater treatment plant is reduced.

Integrated Evaluation Concept to Assess the Efficacy of Advanced Wastewater Treatment Processes for the Elimination of Micropollutants and Pathogens

A multidisciplinary concept has been developed to compare advanced wastewater treatment processes for their efficacy of eliminating micropollutants and pathogens. The concept is based on (i) the removal/formation of selected indicator substances and their transformation products (TPs), (ii) the assessment of ecotoxicity via in vitro tests, and (iii) the removal of pathogens and antibiotic resistant bacteria. It includes substances passing biological wastewater treatment plants regulated or proposed to be regulated in the European Water Framework Directive, TPs formed in biological processes or during ozonation, agonistic/antagonistic endocrine activities, mutagenic/genotoxic activities, cytotoxic activities, further activities like neurotoxicity as well as antibiotics resistance genes, and taxonomic gene markers for pathogens. At a pilot plant, ozonation of conventionally treated wastewater resulted in the removal of micropollutants and pathogens and the reduction of estrogenic effects, whereas the in vitro mutagenicity increased. Subsequent post-treatment of the ozonated water by granular activated carbon (GAC) significantly reduced the mutagenic effects as well as the concentrations of remaining micropollutants, whereas this was not the case for biofiltration. The results demonstrate the suitability of the evaluation concept to assess processes of advanced wastewater treatment including ozonation and GAC by considering chemical, ecotoxicological, and microbiological parameters.

Enhanced membrane bioreactor process without chemical cleaning.

In membrane bioreactors (MBR) for wastewater treatment, the separation of activated sludge and treated water takes place by membrane filtration. Due to the small footprint and superior effluent quality, the number of membrane bioreactors used in wastewater treatment is rapidly increasing. A major challenge in this process is the fouling of the membranes which results in permeability decrease and the demand of chemical cleaning procedures. With the objective of a chemical-free process, the removal of the fouling layer by continuous physical abrasion was investigated. Therefore, particles (granules) were added to the activated sludge in order to realise a continuous abrasion of the fouling layer. During operation for more than 8 months, the membranes showed no decrease in permeability. Fluxes up to 40 L/(m(2) h) were achieved. An online turbidity measurement was installed for the effluent control and showed no change during this test period. For comparison, a reference (standard MBR process without granules) was operated which demonstrated permeability loss at lower fluxes and required chemical cleaning. Altogether with this process an operation at higher fluxes and no use of cleaning chemicals will increase the cost efficiency of the MBR-process.