Water supply development and tariffs in Tanzania: From free water policy towards cost recovery

The article describes the historical development of water tariff policy in Tanzania from the colonial times to present. After gaining independence, the country introduced “free” water policy in its rural areas. Criticism against this policy was expressed already in the 1970s, but it was not until the late 1980s that change became unavoidable. All the while urban water tariffs continued to decline in real terms. In rural and periurban areas of Tanzania consumers often have to pay substantial amounts of money for water to resellers and vendors since the public utilities are unable to provide operative service. Besides, only a part of the water bills are actually collected. Now that the free water supply policy has been officially abandoned, the development of water tariffs and the institutions in general are a great challenge for the country.     

Recovery of gold by chicken egg shell membrane-conjugated chitosan beads

We have successfully prepared a bead-type adsorbent from two materials with different adsorption characteristics. Heavy metals were removed by greatly swollen egg shell membrane-conjugated chitosan beads. The egg shell membrane accumulated and removed precious metal ions from a dilute aqueous solution with a high affinity in a short contact time. Experiments suggested that chitosan beads could take up gold ions with great capacity and selectivity by conjugation with egg shell membrane. Under certain conditions, the selective removal of gold and copper in a mixture of gold and copper ions by egg shell membrane-conjugated chitosan beads was 100% and 2%, respectively. Egg shell membrane-conjugated chitosan beads can be seen as a promising material to recover gold in wastewater from various industries, such as electroplating.     

Nitrogen recovery in an integrated system for wastewater treatment and tilapia production

An integrated system, consisting of Up-flow Anaerobic Sludge Blanket (UASB)-duckweed-tilapia ponds was used for recovery of sewage nutrients and water recycling. A UASB reactor with 40 liter working volume was used as pre-treatment unit followed by a series of three duckweed ponds for nitrogen recovery. The treated effluent and duckweed biomass was used to feed fishponds stocked with Nile tilapia (Oreochromis niloticus). The UASB reactor was fed with raw, domestic sewage at 6 h hydraulic retention time. The three duckweed ponds were stocked with Lemna gibba and fed with UASB effluent at 15 days hydraulic retention time. Nitrogen recovery from UASB effluent via duckweed biomass represented 81% of total nitrogen removal and 46.5% from the total nitrogen input to the system. In subsequent fishponds the nitrogen recovery from duckweed as fish feed was in the range of 13.4–20%. This nitrogen in fish biomass represented 10.6–11.5 g N from the total nitrogen in the raw sewage fed to the UASB reactor. The growth performance of tilapia (Oreochromis niloticus) showed specific growth rates (SGR) in the range of 0.53–0.97. The range of feed conversion ratio (FCR) and protein efficiency ratio (PER) were 1.2–2.2 and 2.1–2.28, respectively. The results of the experiments showed total fish yield and net fish yield in the range of 17–22.8 ton/ha/y and 11.8–15.7 ton/ha/y respectively. In conclusion UASB-duckweed-tilapia ponds provide marketable by-products in the form of duckweed and fish protein, which represent a cost recovery for sewage treatment.     

天然气钻井井口安全距离研究分析

分析天然气钻井井场可能发生的事故类型及事故的破坏程度,选择适合的事故后果模型,对天然气井井喷失控后可能发生的蒸气云爆炸及硫化氢扩散的后果进行量化分析,根据超压-冲量准则、热剂量准则和硫化氢扩散行为规律,计算出爆炸波、爆炸火球及硫化氢扩散的危害范围。笔者建立了天然气钻井井口安全距离的计算模型,并提出一种确定安全距离的方法。通过计算给出不同无阻流量、不同硫化氢体积含量的20种条件下的天然气钻井井口安全距离,并应用该模型对某含硫气井井口安全距离进行了计算。实例表明,该方法具备实用性,值得在天然气井选址规划中推广和使用。     

Recycling and recovery routes for incinerated sewage sludge ash (ISSA): A review

The drivers for increasing incineration of sewage sludge and the characteristics of the resulting incinerated sewage sludge ash (ISSA) are reviewed. It is estimated that approximately 1.7 million tonnes of ISSA are produced annually world-wide and is likely to increase in the future. Although most ISSA is currently landfilled, various options have been investigated that allow recycling and beneficial resource recovery. These include the use of ISSA as a substitute for clay in sintered bricks, tiles and pavers, and as a raw material for the manufacture of lightweight aggregate. ISSA has also been used to form high density glass–ceramics. Significant research has investigated the potential use of ISSA in blended cements for use in mortars and concrete, and as a raw material for the production of Portland cement. However, all these applications represent a loss of the valuable phosphate content in ISSA, which is typically comparable to that of a low grade phosphate ore. ISSA has significant potential to be used as a secondary source of phosphate for the production of fertilisers and phosphoric acid. Resource efficient approaches to recycling will increasingly require phosphate recovery from ISSA, with the remaining residual fraction also considered a useful material, and therefore further research is required in this area.     

Effect of Macroalgal Expansion and Marine Protected Areas on Coral Recovery Following a Climatic Disturbance

Disturbance plays an important role in structuring marine ecosystems, and there is a need to understand how conservation practices, such as the designation of Marine Protected Areas (MPAs), facilitate postdisturbance recovery. We evaluated the association of MPAs, herbivorous fish biomass, substrate type, postdisturbance coral cover, and change in macroalgal cover with coral recovery on the fringing reefs of the inner Seychelle islands, where coral mortality after a 1998 bleaching event was extensive. We visually estimated benthic cover and fish biomass at 9 sites in MPAs where fishing is banned and at 12 sites where fishing is permitted in 1994, 2005, 2008, and 2011. We used analysis of variance to examine spatial and temporal variations in coral cover and generalized additive models to identify relations between coral recovery and the aforementioned factors that may promote recovery. Coral recovery occurred on all substrate types, but it was highly variable among sites and times. Between 2005 and 2011 the increase in coral cover averaged 1%/year across 21 sites, and the maximum increase was 4%/year. However, mean coral cover across the study area (14%) remained at half of 1994 levels (28%). Sites within MPAs had faster rates of coral recovery than sites in fished areas only where cover of macroalgae was low and had not increased over time. In MPAs where macroalgae cover expanded since 1998 there was no recovery. Where coral was recovering on granite reefs there was a shift in relative prevalence of colony life‐form from branching to encrusting species. This simplification of reef structure may affect associated reef fauna even if predisturbance levels of coral cover are attained. Efecto de la Expansión de Macroalgas y Áreas Marinas Protegidas sobre la Recuperación de Coral Después de una Perturbación Climática     

Intraspecific Chromosome Number Variation: a Neglected Threat to the Conservation of Rare Plants

Abstract: The effectiveness of rare plant conservation will increase when life history, demographic, and genetic data are considered simultaneously. Inbreeding depression is a widely recognized genetic concern in rare plant conservation, and the mixing of genetically diverse populations in restoration efforts is a common remedy. Nevertheless, if populations with unrecognized intraspecific chromosome variation are crossed, progeny fitness losses will range from partial to complete sterility, and reintroductions and population augmentation of rare plants may fail. To assess the current state of cytological knowledge of threatened and endangered plants in the continental United States, we searched available resources for chromosome counts. We also reviewed recovery plans to discern whether recovery criteria potentially place listed species at risk by requiring reintroductions or population augmentation in the absence of cytological information. Over half the plants lacked a chromosome count, and when a taxon did have a count it generally originated from a sampling intensity too limited to detect intraspecific chromosome variation. Despite limited past cytological sampling, we found 11 plants with documented intraspecific cytological variation, while 8 others were ambiguous for intraspecific chromosome variation. Nevertheless, only one recovery plan addressed the chromosome differences. Inadequate within‐species cytological characterization, incomplete sampling among listed taxa, and the prevalence of interspecific and intraspecific chromosome variation in listed genera, suggests that other rare plants are likely to have intraspecific chromosome variation. Nearly 90% of all recovery plans called for reintroductions or population augmentation as part of recovery criteria despite the dearth of cytological knowledge. We recommend screening rare plants for intraspecific chromosome variation before reintroductions or population augmentation projects are undertaken to safeguard against inadvertent mixtures of incompatible cytotypes.     

植物修复及强化调控系统根际土壤微生物研究综述

根际土壤微生物是植物修复及其强化修复技术的重要组成部分,了解根际土壤微生物生态效应有助于深入探索修复机制,从而进一步提高修复效率.微生物生态效应反映土壤生态变化,对于有效评估强化调控生态风险具有重要意义.在总结污染土壤植物修复根际微生物生态效应研究的基础上,综述强化调控措施与根际土壤微生物可能存在的相互影响,并分析利用微生物分子生态学技术评估强化调控措施施用风险的可行性.     

An easy method to design gas/vapor relief system with rupture disk

Tank discharge gas/vapor flow problems are frequently encountered in both practice and design. To perform this type of design calculation, the first step is to identify whether the flow is choked or not through a trial-and-error solution of an equation for adiabatic flow with friction from a reservoir through a pipe. Developing a direct method without any trial-and-error to identify a choking condition would be helpful for expediting the flow calculations. This paper presents an easy and quick method to identify the choking of gas flow for an emergency relief system consisting of a rupture disk and vent piping. This greatly simplifies the design calculations. The proposed method for validating the venting adequacy of existing ERS circumvents the iteration calculation and the use of Lapple charts. Three case studies for the design of vent piping for rupture disks support the proposed method.     

Thinking with salmon about rain tanks: commons as intra-actions

The construction of California's large waterworks was inextricably entangled with a discourse of progress through technoscientific control over unruly rivers. In recent years, a turn towards decentralised governance and diversified infrastructure has produced alternate discourses of human–ecological collaboration and water as a commons. I investigate how water is understood by residents along Salmon Creek (Sonoma Co., CA) engaged in efforts to increase streamflow and restore salmon runs. Drawing on Barad's theory of agential realism, I find that living with springs and rainwater harvesting cisterns enacts intra-actions that increase residents' sense of interdependence with other human and nonhuman watershed residents. I argue that commons frameworks represent a coherent alternative to state and market frameworks of water governance.