Socio-environmental consideration of phosphorus flows in the urban sanitation chain of contrasting cities

Understanding how cities can transform organic waste into a valuable resource is critical to urban sustainability. The capture and recycling of phosphorus (P), and other essential nutrients, from human excreta is particularly important as an alternative organic fertilizer source for agriculture. However, the complex set of socio-environmental factors influencing urban human excreta management is not yet sufficiently integrated into sustainable P research. Here, we synthesize information about the pathways P can take through urban sanitation systems along with barriers and facilitators to P recycling across cities. We examine five case study cities by using a sanitation chains approach: Accra, Ghana; Buenos Aires, Argentina; Beijing, China; Baltimore, USA; and London, England. Our cross-city comparison shows that London and Baltimore recycle a larger percentage of P from human excreta back to agricultural lands than other cities, and that there is a large diversity in socio-environmental factors that affect the patterns of recycling observed across cities. Our research highlights conditions that may be “necessary but not sufficient” for P recycling, including access to capital resources. Path dependencies of large sanitation infrastructure investments in the Global North contrast with rapidly urbanizing cities in the Global South, which present opportunities for alternative sanitation development pathways. Understanding such city-specific social and environmental barriers to P recycling options could help address multiple interacting societal objectives related to sanitation and provide options for satisfying global agricultural nutrient demand.

     

A comparison of results from two test methods for assessing the toxicity of aminotriazole to Selenastrum capricornutum

Two different test methods for assessing the toxicity of aminotriazole to Selenastrum capricornutum are compared. Growth medium composition is demonstrated to have a significant effect on the toxicity of aminotriazole.     

Anaerobic co-digestion of swine and poultry manure with municipal sewage sludge

The anaerobic digestion of municipal sewage sludge (SS) with swine manure (SM) and poultry manure (PM) was undertaken. It was found that a mixture of sewage sludge with a 30% addition of swine manure gave around 400 dm³/kgVS of biogas, whereas the maximal biogas yield from ternary mixture (SS:SM:PM = 70:20:10 by weight) was only 336 dm³/kgVS. An inhibition of methanogenesis by free ammonia was observed in poultry manure experiments. The anaerobic digestion was inefficient in pathogen inactivation as the reduction in the number of E. coli an Enterobacteriaceae was only by one logarithmic unit. A substantial portion of pathogens was also released into the supernatant.     

Effect of compost treatment of sewage sludge on nitrogen behavior in two soils

This work aims to evaluate the effects of compost treatment of digested sewage sludge on nitrogen behavior in two soils, a Spodosol and an Oxisol soil. Digested sewage sludge was composted with sawdust and woodchips, diluting the total nitrogen to one-fourth (dry mass basis) of its original value. Then, sludge and compost were added to the two soils on an equivalent dry weight basis to consider the risk of NO3- -N leaching. Compost treatment of sewage sludge has slowed down the release of mineral-N to half in the Spodosol and to one-third in Oxisol soil. As a result, NO3- -N concentrations in soils incubated with compost were less than half of the amounts found from soils incubated with digested sludge. Estimates were made of the maximum monthly nitrate to leach from the four combinations of soil and sludge treatment. Application of digested sludge, at a higher nitrogen application rate, resulted in a higher nitrate leaching potential than application of the compost product. Soil type also played an important role, with the Oxisol having slightly higher estimated leaching potential than the Spodosol. The higher nitrate release rate in the Oxisol is counterbalanced by its higher field capacity to lessen the expected difference between the two soils.     

Restoring acidified streams in upland Wales: a modelling comparison of the chemical and biological effects of liming and reduced sulphate deposition

Increasing emphasis is being placed on the restoration of surface waters which have been affected by acidification. Amongst the possible strategies are management of the causes, by reducing acidic deposition, and management of the symptoms, by treating affected areas with basic material such as limestone. In few cases have there been comparisons of the likely effect of these two strategies on surface water chemistry and ecology, although there is widespread belief that the two are similar in outcome. At present, only a modelling approach permits such a comparison. This paper describes chemical and biological responses of three Welsh streams whose catchments were limed experimentally in 1987-1988 as part of the Llyn Brianne project. Actual changes are compared with simulated changes which occur following reduced acid deposition according to the hydrochemical model, MAGIC (Model of Acidification of Groundwaters in Catchments). The results indicate that liming and 90% reduction in sulphate deposition reduce concentrations of toxic aluminium to similar levels. However, calcium concentrations and pH were increased by liming to values which were high by comparison with conditions simulated at low acid deposition, either in the past or future. Trout density increased in two of the streams following liming to levels similar to those simulated under low acid deposition. By contrast, the aquatic invertebrate fauna changed after liming so that streams acquired species typical of higher calcium concentrations than those simulated under low acid deposition. Species characteristic of 'soft water' communities were apparently lost, although more data are required to separate treatment effects from random change in the longer term. The 'soft water' community also declined in the model as a result of acidification, indicating that both liming and acid deposition resulted in a different faunal community from that prior to acidification. The results support those who conclude that liming is suitable for the restoration or protection of a fishery, but indicate that there may be other ramifications, for example to conservation, which must be considered when liming is implemented. However, the simulation of biological conditions under low acid deposition involves extrapolation from the initial data base. Further data are now required to assess empirically the likely biological character of British streams which have low base cation concentrations unaffected by acid deposition.     

Octachlorodibenzo-p-dioxin in wood treatment materials and treated wood

The octachlorodibenzo-p-dioxin (OCDD) concentrations have been determined in aged samples of commercial pentachlorophenol (PCP), in wood protection formulations containing PCP and in wood treated with PCP as a preservative or as an anti-sapstain treatment. The concentrations of OCDD found in the various samples are within the range expected from the amount of commercial PCP initially present in the samples. In view of the known stability of OCDD the results are interpreted as indicating that the formulation, treatment and ageing processes have not led to any substantial conversion of PCP to OCDD; although one result indicates that outdoor exposure of treated samples increased the OCDD concentration by a factor of approximately 2 after $\text{3}\text{1}\text{2}$ years. Analysis of aged samples of treated wood indicate that OCDD is lost much less rapidly from the wood than PCP.     

Polychlorinated biphenyls and organochlorine pesticides in EELS (Anguilla anguilla L.) from Welsh rivers

Organochlorine concentrations in the muscle tissues of eels at 41 freshwater sites across Wales were surveyed in 1993. Positive but weak relationships were detected between eel age or length and the concentration of some organochlorines. Isomers of HCH were below detection at most sites. Dieldrin was widespread at 10-100 microg kt(-1) wet weight, despite its ban in sheep dip in 1989. Total DDT residue concentrations averaged 73 microg kg(-1). Total PCB burdens expressed as Arochlor 1260, were > 50 microg kg(-1) at 76% of sites and > 100 microg kg(-1) at 46% of sites. The range of concentrations was comparable with other UK data. Rural sites had relatively low levels of PCBs, highest contamination occurring in the lower reaches of industrialised catchments. The inferences for environmental effects are discussed.     

Analysis of polychlorobiphenyls from used transformers for polychlorodibenzofurans

The results of analyses for polychlorodibenzofuran (PCDF) content in two samples of polychlorobiphenyl (PCB) from used electrical transformers are presented and discussed. In neither sample was there evidence for enhanced PCDF concentrations even though one of them had been subjected to overheating while in service.     

Polychlorodibenzo-p-dioxins and dibenzofurans in technical pentachlorophenol - results of a collaborative analytical exercise

Results of analyses of eight samples of technical pentachlorophenol conducted by three different analytical methods are presented and discussed.