Evaluation of harvesting urban water resources for sustainable water management: Case study in Filton Airfield, UK.

Filton Airfield in the UK is a new community under development aiming to become self-sufficient in its water supply toward a circular economy. Urban water management strategies, water demand minimization, urban resource reuse, and wastewater discharge minimization, can improve the urban circular economy. Understanding the practical impacts of those strategies is crucial for a new development area like Filton. As a site investigation, the physiochemical and microbial characteristics of raw rainwater showed acceptable for irrigation and drinking water, indicating no significant risk of using rainwater collected within Filton, but still requiring a treatment process depending on chosen applications. This study further conducted stochastic water demand profiles and urban water cycle simulations at a block scale, taking possible rainwater harvesting (RWH) and greywater recycling (GWR) options for non-potable purposes to quantitatively assess the impact of urban water management strategies on urban harvesting potential indicators (0-100%). When the RWH was implemented, the water demand minimization potential varied from 62% to 71%. Meanwhile, the combined use of RWH and GWR yielded even better results in terms of water demand minimization, peaking at 78% due to the additional supply from GWR. The combination also reduced wastewater production potential from 100% to 54% and consequently improves self-sustainability potential from 0 with no recycling, to 44% with only GWR, and to 100% with the combined use of RWH and GWR. The sensitivity analysis revealed that wastewater discharge is the most sensitive to variations in rainfall patterns (wet and dry conditions) and urban density (water demand patterns), indicating that both need to be balanced for better implementation of urban water harvesting strategies. This study can provide insights into the applicability of urban water resource harvesting and its assessment approaches in existing and new development areas.

Optimal storage sizing for indoor arena rainwater harvesting: Hydraulic simulation and economic assessment.

This study demonstrates a large roof (30,000 m2) rainwater harvesting (RWH) system in an indoor arena by considering three water demand scenarios (toilet flushing, irrigation and combined demand) via hydraulic and economic assessments. The water saving efficiency (WSE) of the RWH system for each scenario was estimated by a simulation model using historical daily rainfall data (1968-2018). Depending on the water demand, the WSE was found to be independent of tank size when the tank size exceeded 1000 m3. The results suggest that the WSE of the RWH system is highly influenced by water demand scenarios, and a storage capacity of 400-1000 m3 would be enough for the applications considered in this study. The economic analysis results further showed that depending on the water demand, the RWH system with a rainwater storage capacity of between 100 and 600 m3 was more economically beneficial due to its positive cost saving values. The results also showed that depending on the water scenarios, the unit water cost between 0.37 and 0.40 £/m3 was lower than the mains water cost (0.40 £/m3). As a result, the use of the RWH system with a tank between 400 and 600 m3 can be the most favourable range under the conditions considered in this study. Given the variations in water price, rainfall patterns and discount rates, the sensitivity analysis showed that water tariffs and discount rates play a significant role in reducing the unit water cost of the system, maintaining it lower than the mains water cost. A payback period analysis of the RWH system with a 600 m3 tank revealed that a 5% discount rate and a water price of 3 £/m3 would be enough to make the RWH system cost effective and that the capital cost could be returned within 10-11 years. This study highlights the need for preliminary sizing of a rainwater tank and an economic analysis of a large rooftop RWH system to maximise the benefits.

Young people's perception of sexual and reproductive health services in Kenya.

BACKGROUND: Addressing the Sexual and Reproductive Health (SRH) needs of young people remains a big challenge. This study explored experiences and perceptions of young people in Kenya aged 10-24 with regard to their SRH needs and whether these are met by the available healthcare services. METHODS: 18 focus group discussions and 39 in-depth interviews were conducted at health care facilities and youth centres across selected urban and rural settings in Kenya. All interviews were tape recorded and transcribed. Data was analysed using the thematic framework approach. RESULTS: Young people's perceptions are not uniform and show variation between boys and girls as well as for type of service delivery. Girls seeking antenatal care and family planning services at health facilities characterise the available services as good and staff as helpful. However, boys perceive services at health facilities as designed for women and children, and therefore feel uncomfortable seeking services. At youth centres, young people value the non-health benefits including availability of recreational facilities, prevention of idleness, building of confidence, improving interpersonal communication skills, vocational training and facilitation of career progression. CONCLUSION: Providing young people with SRH information and services through the existing healthcare system, presents an opportunity that should be further optimised. Providing recreational activities via youth centres is reported by young people themselves to not lead to increased uptake of SRH healthcare services. There is need for more research to evaluate how perceived non-health benefits young people do gain from youth centres could lead to improved SRH of young people.

A bottom-up approach to estimate dry weather flow in minor sewer networks.

In order to evaluate the feasibility of installing decentralised installations for wastewater reuse in cities, information about flows at specific spots of a sewer is needed. However, measuring intermittent flows in partially filled conduits is a technical task which is sometimes difficult to accomplish. This paper describes a method to model intermittent discharges in small sewers by linking a stochastic model for wastewater discharge to a hydraulic model to predict the attenuation of the discharges and its impact on the arrival time to a defined spot. The method was validated in a case study. The model estimated adequately the wastewater discharges on working days.

A perceptual approach to address complex water management issues in lowland permeable catchments.

Water quality management is a pressing global concern, and an increasingly complex issue due to climate and land-use change, legacy pollution, and the persistent release of well-known and emerging contaminants from diffuse and point sources. The increasing availability of high-frequency monitoring data is leading existing, often heuristic approaches, to be judged inadequate. Water managers frequently rely on simple qualitative and/or quantitative approaches for decision-making, but a lack of tangible improvement in freshwater quality outcomes is demanding new and innovative approaches that rely more on physical process understanding, rather than precedent. In this study, we drew upon local geological, hydrogeological, and hydrological data to infer a high-level perceptual model of surface/groundwater interactions in a chalk stream in Dorset, UK. We used the perceptual model to interrogate spatial and temporal trends in historical water quality data and to construct reach-scale nutrient mass balances. Through novel representation with Sankey diagrams, the perceptual model highlighted the relative importance of different hydrological features. Surface/groundwater interactions were found to occur predominantly by spring flow. We demonstrate that river flow accretion was dominated by the Chalk aquifer despite only occupying ca. 15 % of the surface bedrock area, and that spring sources, whilst vital to dilute treated sewage inputs in baseflow conditions, were also major sources of legacy nitrate. Nutrient mass balances showed that sewage treatment works contributed ca. 13 % to soluble reactive phosphorus load, with groundwater accounting for ca. 48 %. Thus, a determinand often associated with point-source pollution was shown to be diffuse dominated in this river. The study demonstrated how a multi-disciplinary approach to water management, based on a comprehensive perceptual modelling approach, could identify hitherto unknown sources and relative contributors to freshwater pollution and allow flow and load apportionment studies to provide useful decision-support to manage nutrient pollution. The novel application of perceptual modelling tools, such as the Sankey diagram, allows different source attributions to be presented in an accessible manner, and can be readily transferred to other study areas.

Sexual reproductive health service provision to young people in Kenya; health service providers' experiences.

BACKGROUND: Addressing the sexual and reproductive health (SRH) needs of young people remains a challenge for most developing countries. This study explored the perceptions and experiences of Health Service Providers (HSP) in providing SRH services to young people in Kenya. METHODS: Qualitative study conducted in eight health facilities; five from Nairobi and three rural district hospitals in Laikipia, Meru Central, and Kirinyaga. Nineteen in-depth interviews (IDI) and two focus group discussions (FGD) were conducted with HSPs. Interviews were tape recorded and transcribed. Data was coded and analysed using the thematic framework approach. RESULTS: The majority of HSPs were aware of the youth friendly service (YFS) concept but not of the supporting national policies and guidelines. HSP felt they lacked competency in providing SRH services to young people especially regarding counselling and interpersonal communication. HSPs were conservative with regards to providing SRH services to young people particularly contraception. HSP reported being torn between personal feelings, cultural and religious values and beliefs and their wish to respect young people's rights to accessing and obtaining SRH services. CONCLUSION: Supporting youth friendly policies and competency based training of HSP are two common approaches used to improve SRH services for adolescents. However, these may not be sufficient to change HSPs' attitude to adolescents seeking help. There is need to address the cultural, religious and traditional value systems that prevent HSPs from providing good quality and comprehensive SRH services to young people. Training updates should include sessions that enable HSPs to evaluate how their personal and cultural values and beliefs influence practice.

Wastewater monitoring for detection of public health markers during the COVID-19 pandemic: Near-source monitoring of schools in England over an academic year.

BACKGROUND: Schools are high-risk settings for infectious disease transmission. Wastewater monitoring for infectious diseases has been used to identify and mitigate outbreaks in many near-source settings during the COVID-19 pandemic, including universities and hospitals but less is known about the technology when applied for school health protection. This study aimed to implement a wastewater surveillance system to detect SARS-CoV-2 and other public health markers from wastewater in schools in England. METHODS: A total of 855 wastewater samples were collected from 16 schools (10 primary, 5 secondary and 1 post-16 and further education) over 10 months of school term time. Wastewater was analysed for SARS-CoV-2 genomic copies of N1 and E genes by RT-qPCR. A subset of wastewater samples was sent for genomic sequencing, enabling determination of the presence of SARS-CoV-2 and emergence of variant(s) contributing to COVID-19 infections within schools. In total, >280 microbial pathogens and >1200 AMR genes were screened using RT-qPCR and metagenomics to consider the utility of these additional targets to further inform on health threats within the schools. RESULTS: We report on wastewater-based surveillance for COVID-19 within English primary, secondary and further education schools over a full academic year (October 2020 to July 2021). The highest positivity rate (80.4%) was observed in the week commencing 30th November 2020 during the emergence of the Alpha variant, indicating most schools contained people who were shedding the virus. There was high SARS-CoV-2 amplicon concentration (up to 9.2x106 GC/L) detected over the summer term (8th June - 6th July 2021) during Delta variant prevalence. The summer increase of SARS-CoV-2 in school wastewater was reflected in age-specific clinical COVID-19 cases. Alpha variant and Delta variant were identified in the wastewater by sequencing of samples collected from December to March and June to July, respectively. Lead/lag analysis between SARS-CoV-2 concentrations in school and WWTP data sets show a maximum correlation between the two-time series when school data are lagged by two weeks. Furthermore, wastewater sample enrichment coupled with metagenomic sequencing and rapid informatics enabled the detection of other clinically relevant viral and bacterial pathogens and AMR. CONCLUSIONS: Passive wastewater monitoring surveillance in schools can identify cases of COVID-19. Samples can be sequenced to monitor for emerging and current variants of concern at the resolution of school catchments. Wastewater based monitoring for SARS-CoV-2 is a useful tool for SARS-CoV-2 passive surveillance and could be applied for case identification and containment, and mitigation in schools and other congregate settings with high risks of transmission. Wastewater monitoring enables public health authorities to develop targeted prevention and education programmes for hygiene measures within undertested communities across a broad range of use cases.

Monitoring occurrence of SARS-CoV-2 in school populations: A wastewater-based approach.

Clinical testing of children in schools is challenging, with economic implications limiting its frequent use as a monitoring tool of the risks assumed by children and staff during the COVID-19 pandemic. Here, a wastewater-based epidemiology approach has been used to monitor 16 schools (10 primary, 5 secondary and 1 post-16 and further education) in England. A total of 296 samples over 9 weeks have been analysed for N1 and E genes using qPCR methods. Of the samples returned, 47.3% were positive for one or both genes with a detection frequency in line with the respective local community. WBE offers a low cost, non-invasive approach for supplementing clinical testing and can provide longitudinal insights that are impractical with traditional clinical testing.

Water and energy as inseparable twins for sustainable solutions.

Although the water cycle is only a minor contributor to the energy demand in society, it is a matter of good housekeeping to minimize the energy need within a sustainable water cycle. Wastewater treatment should not only be applied to purify the water, but also recover the energy present in this water, as well as to recover essential elements like nitrogen and phosphorus. From an energy analysis of the Dutch water cycle it is concluded that creating an energy neutral water cycle by using the heat content or by making use of the organic load of wastewater is within hands.

From pollutant removal to resource recovery: A bibliometric analysis of municipal wastewater research in Europe.

Municipal wastewaters are abundant low-strength streams that require adequate treatment and disposal to ensure public and environmental health. This study aims to provide a comprehensive summary of municipal wastewater research in Europe in the 2010s in the form of bibliometric analysis. The work was based on the Science Citation Index Expanded (Web of Science) and carried out using the R-package bibliometrix for bibliometric data analysis and the software VOSviewer for science mapping. Analysing a dataset of 5645 publications, we identified the most influential journals, countries, authors, institutions, and publications, and mapped the co-authorship and keyword co-occurrence networks. Spain had produced the most publications while Switzerland had the highest average citations per publication. China was the most collaborative country from outside of Europe. Analysis of the most cited articles revealed the popularity of micropollutant removal in European municipal wastewater research. The keyword analysis visualized a paradigm shift from pollutant removal towards resource recovery and circular economy. We found that current challenges of resource recovery from municipal wastewater come from both technical and non-technical (e.g., environmental, economic, and social) aspects. We also discussed future research opportunities that can tackle these challenges.

Making Waves: Collaboration in the time of SARS-CoV-2 - rapid development of an international co-operation and wastewater surveillance database to support public health decision-making.

The presence of SARS-CoV-2 RNA in wastewater was first reported in March 2020. Over the subsequent months, the potential for wastewater surveillance to contribute to COVID-19 mitigation programmes has been the focus of intense national and international research activities, gaining the attention of policy makers and the public. As a new application of an established methodology, focused collaboration between public health practitioners and wastewater researchers is essential to developing a common understanding on how, when and where the outputs of this non-invasive community-level approach can deliver actionable outcomes for public health authorities. Within this context, the NORMAN SCORE "SARS-CoV-2 in sewage" database provides a platform for rapid, open access data sharing, validated by the uploading of 276 data sets from nine countries to-date. Through offering direct access to underpinning meta-data sets (and describing its use in data interpretation), the NORMAN SCORE database is a resource for the development of recommendations on minimum data requirements for wastewater pathogen surveillance. It is also a tool to engage public health practitioners in discussions on use of the approach, providing an opportunity to build mutual understanding of the demand and supply for data and facilitate the translation of this promising research application into public health practice.

Availability, utilisation and quality of basic and comprehensive emergency obstetric care services in Malawi.

OBJECTIVE: To establish a baseline for the availability, utilisation and quality of maternal and neonatal health care services for monitoring and evaluation of a maternal and neonatal morbidity/mortality reduction programme in three districts in the Central Region of Malawi. METHODS: Survey of all the 73 health facilities (13 hospitals and 60 health centres) that provide maternity services in the three districts (population, 2,812,183). RESULTS: There were 1.6 comprehensive emergency obstetric care (CEmOC) facilities per 500,000 population and 0.8 basic emergency obstetric care (BEmOC) facilities per 125,000 population. About 23% of deliveries were conducted in emergency obstetric care (EmOC) facilities and the met need for emergency obstetric complications was 20.7%. The case fatality rate for emergency obstetric complications treated in health facilities was 2.0%. Up to 86.7% of pregnant women attended antenatal clinic at least once and only 12.0% of them attend postnatal clinic at least once. There is a shortage of qualified staff and unequal distribution with more staff in hospitals leaving health centres severely understaffed. CONCLUSIONS: The total number of CEmOC facilities is adequate but the distribution is unequal, leaving some rural areas with poor access to CEmOC services. There are no functional BEmOC facilities in the three districts. In order to reduce maternal mortality in Malawi and countries with similar socio-economic profile, there is a need to upgrade some health facilities to at least BEmOC level by training staff and providing equipment and supplies.

Global Sensitivity Analysis of Metabolic Models for Phosphorus Accumulating Organisms in Enhanced Biological Phosphorus Removal.

The aim of this study was to identify, quantify and prioritize for the first time the sources of uncertainty in a mechanistic model describing the anaerobic-aerobic metabolism of phosphorus accumulating organisms (PAO) in enhanced biological phosphorus removal (EBPR) systems. These wastewater treatment systems play an important role in preventing eutrophication and metabolic models provide an advanced tool for improving their stability via system design, monitoring and prediction. To this end, a global sensitivity analysis was conducted using standard regression coefficients and Sobol sensitivity indices, taking into account the effect of 39 input parameters on 10 output variables. Input uncertainty was characterized with data in the literature and propagated to the output using the Monte Carlo method. The low degree of linearity between input parameters and model outputs showed that model simplification by linearization can be pursued only in very well defined circumstances. Differences between first and total-order sensitivity indices showed that variance in model predictions was due to interactions between combinations of inputs, as opposed to the direct effect of individual inputs. The major sources of uncertainty affecting the prediction of liquid phase concentrations, as well as intra-cellular glycogen and poly-phosphate was due to 64% of the input parameters. In contrast, the contribution to variance in intra-cellular PHA constituents was uniformly distributed among all inputs. In addition to the intra-cellular biomass constituents, notably PHB, PH2MV and glycogen, uncertainty with respect to input parameters directly related to anaerobic propionate uptake, aerobic poly-phosphate formation, glycogen formation and temperature contributed most to the variance of all model outputs. Based on the distribution of total-order sensitivities, characterization of the influent stream and intra-cellular fractions of PHA can be expected to significantly improve model reliability. The variance of EBPR metabolic model predictions was quantified. The means to account for this variance, with respect to each quantity of interest, given knowledge of the corresponding input uncertainties, was prescribed. On this basis, possible avenues and pre-requisite requirements to simplify EBPR metabolic models for PAO, both structurally via linearization, as well as by reduction of the number of non-influential variables were outlined.

New framework for automated article selection applied to a literature review of Enhanced Biological Phosphorus Removal.

AIMS: Enhanced Biological Phosphorus Removal (EBPR) is a technology widely used in wastewater treatment to remove phosphorus (P) and prevent eutrophication. Establishing its operating efficiency and stability is an active research field that has generated almost 3000 publications in the last 40 years. Due to its size, including over 119 review articles, it is an example of a field where it becomes increasingly difficult to manually recognize its key research contributions, especially for non-experts or newcomers. Therefore, this work included two distinct but complementary objectives. First, to assemble for the first time a collection of bibliometric techniques into a framework for automating the article selection process when preparing a literature review (section 2). Second, to demonstrate it by applying it to the field of EBPR, producing a bibliometric analysis and a review of the key findings of EBPR research over time (section 3). FINDINGS: The joint analysis of citation networks, keywords, citation profiles, as well as of specific benchmarks for the identification of highly-cited publications revealed 12 research topics. Their content and evolution could be manually reviewed using a selection of articles consisting of approximately only 5% of the original set of publications. The largest topics addressed the identification of relevant microorganisms, the characterization of their metabolism, including denitrification and the competition between them (Clusters A-D). Emerging and influential topics, as determined by different citation indicators and temporal analysis, were related to volatile fatty acid production, P-recovery from waste activated sludge and aerobic granules for better process efficiency and stability (Clusters F-H). CONCLUSIONS: The framework enabled key contributions in each of the constituent topics to be highlighted in a way that may have otherwise been biased by conventional citation-based ranking. Further, it reduced the need for manual input and a priori expertise compared to a traditional literature review. Hence, in an era of accelerated production of information and publications, this work contributed to the way that we are able to use computer-aided approaches to curate information and manage knowledge.

Correction: New framework for automated article selection applied to a literature review of Enhanced Biological Phosphorus Removal.

[This corrects the article DOI: 10.1371/journal.pone.0216126.].

Motorcycle ambulances for referral of obstetric emergencies in rural Malawi: do they reduce delay and what do they cost?

OBJECTIVES: To assess whether motorcycle ambulances placed at rural health centers are a more effective method of reducing referral delay for obstetric emergencies than a car ambulance at the district hospital, and to compare investment and operating costs with those of a 4 wheel drive car ambulance at the district hospital. METHODS: Motorcycle ambulances were placed at 3 remote rural health centers in Malawi. Data were collected over a 1-year period, from October 2001 to September 2002, using logbooks, cashbooks, referral forms, and maternity registers. RESULTS: Depending on the site, median referral delay was reduced by 2-4.5 hours (35%-76%). Purchase price of a motorcycle ambulance was 19 times cheaper than for a car ambulance. Annual operating costs were US dollars 508, which was almost 24 times cheaper than for a car ambulance. CONCLUSIONS: In resource-poor countries motorcycle ambulances at rural health centers are a useful means of referral for emergency obstetric care and a relatively cheap option for the health sector.

Peripheral and axial substitution of phthalocyanines with solketal groups: synthesis and in vitro evaluation for photodynamic therapy.

Phthalocyanines (Pcs) are a class of photosensitizers (PSs) with a strong tendency to aggregate in aqueous environment, which has a negative influence on their photosensitizing ability in photodynamic therapy. Pcs with either peripheral or axial solketal substituents, that is, ZnPc(sol)8 and Si(sol)2Pc, respectively, were synthesized and their tendency to aggregate as well as their photodynamic properties in 14C and B16F10 cell lines were evaluated. The results were compared to more hydrophilic silicon Pcs, that is, Si(PEG750)2Pc and Pc4. The order of cellular uptake was Pc4 > ZnPc(sol)8 > Si(PEG750)2Pc > Si(sol2)Pc. In contrast, Si(sol2)Pc showed the highest photocytotoxicity, while ZnPc(sol)8 did not show any photocytotoxicity up to a concentration of 10 microM in both cell types. UV/vis spectroscopy showed that Si(sol)2Pc is less prone to aggregation than ZnPc(sol)8, which can explain the lack of photoactivity of the latter. Si(sol)2Pc was predominantly located in lipid droplets, whereas Si(PEG750)2Pc was homogeneously distributed in the cytosol, which is probably the main cause of their difference in photoactivity. The very high photodynamic efficacy of Si(sol)2Pc makes this PS an interesting candidate for future studies.

A criteria-based clinical audit on the case-management of children presenting with malaria at Mangochi District Hospital, Malawi.

Malaria is a major threat to global health and is one of the leading causes of death worldwide. It is estimated that 2.3 billion people live in areas of malaria risk and each year 300-500 million cases of Plasmodium falciparum malaria occur worldwide. This parasitic infection is one of the major causes of morbidity and mortality in Africa and approximately 90% of cases which include life-threatening malaria are in children, the highest mortality rate being found in children under the age of five. Improvement in case-management of malaria in children is one of the strategies in the prevention of infant mortality. In particular, the health system needs to concentrate on good quality care at the first referral level of the district hospital, as health care provided at this level is crucial for reducing child mortality and for a credible and effective support for the primary health care system. The conduct of systematic assessments of clinical care of malaria including the diagnostic process, medical treatment and nursing care in order to reveal shortcomings in case-management and make improvements are vital. Clinical audit is now routinely used and accepted as part of quality assurance in the health care services of many developed countries, but it has yet to be widely applied to the developing world. The principal objective of the study conducted, was therefore to assess the clinical care of children with malaria at district hospital level in a low-income African country to highlight potential areas of improvement in the quality of care of malaria. At the same time, the specific objectives involved: Assessment of diagnostic process, medical treatment and nursing care; Identification of strengths and deficiencies in current practice; Identification of factors contributing to poor quality of care; Finding strategies to improve current practice.

Is there evidence for man-made nanoparticles in the Dutch environment?

Only very limited information is available on measured environmental concentrations of nanoparticles. In this study, several environmental compartments in The Netherlands were probed for the presence of nanoparticles. Different types of water were screened for the presence of inorganic (Ag, Au, TiO2) and organic nanoparticles (C60, C70, [6,6]-phenyl-C61-butyric acid octyl ester, [6,6]-phenyl-C61-butyric acid butyl ester, [6,6]-phenyl-C61-butyric acid methyl ester, [6,6]-bis-phenyl-C61-butyric acid methyl ester, [6,6]-phenyl-C71-butyric acid methyl ester, [6,6]-thienyl-C61-butyric acid methyl ester). Air samples were analysed for the presence of nanoparticulate Mo, Ag, Ce, W, Pd, Pt, Rh, Zn, Ti, Si, B as well as Fe and Cu. ICP-MS, Orbitrap-HRMS, SEM and EDX were used for this survey. Water samples included dune and bank filtrates, surface waters and ground waters as well as influents, effluents and sludge of sewage treatment plants (STPs), and surface waters collected near airports and harbours. Air samples included both urban and rural samples. C60 was detected in air, sewage treatment plants, influents, effluents and sludge, but in no other aqueous samples despite the low detection limit of 0.1ng/L. C70 and functionalised fullerenes were not detected at all. In STP sludge and influent the occurrence of Ag and Au nanoparticles was verified by SEM/EDX and ICP-MS. In air up to about 25m% of certain metals was found in the nanosize fraction. Overall, between 1 and 6% of the total mass from metals in the air samples was found in the size fraction <100nm.

Permeability determination through NMR detection of acoustically induced fluid oscillation.

We present a novel approach for directly measuring the permeability of reservoir rocks by an instrument lowered in a well bore. The measurement is made by creating an oscillatory motion of fluids in the pores by acoustic stimulation and by detecting the amplitude response as a phase shift on a nuclear magnetic resonance relaxation signal. A full theoretical description is given. The feasibility of the method has been verified in the laboratory on a set of sandstone and carbonate samples spanning the entire range of practical interest.