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The effects of municipal sludge compost (MSC) as a soil amendment are often studied in agricultural soil or topsoil contaminated with heavy metals. However, little is known about the effects of MSC amendments on plant growth and heavy metal bioavailability in subsoil. This study was conducted to investigate the effects of MSC application on plant growth and the mobility and bioavailability of Cd, Cu, and Zn in an amended soil-plant system. A pot experiment was performed to evaluate the translocation of heavy metals to broad bean (Vicia faba L.) grown in loess subsoil previously amended with different application rates of MSC. The subsoil and MSC were homogeneously mixed to achieve six soil-amended treatments (total weight of 8 kg in each pot) in 0, 0.5, 2, 6, 15, and 30% mass ratios (MSC/total). Soil samples amended with MSC were aged for 60 days before sowing. Soil and plant samples were collected after 120 days of growth. Plant height was periodically measured until harvest. The total quantities of heavy metals and their different fractions were analyzed by using graphite furnace atomic absorption spectroscopy (GF-AAS). Compared with the control soil (0% treatment), the average biomass growth rates from the 0.5 to 30% treatments ranged from 14.5 to 170.4% (increasing order), respectively. Cd (0.42–1.85 mg kg−1) and Cu (14.95–23.01 mg kg−1) mainly concentrated in the plant roots, and Zn (22.06–36.48 mg kg−1) mainly concentrated in the plant stems and leaves. Fortunately, the metal concentrations in the edible plant parts (0.03–0.1 mg kg−1) remained below the Chinese national standard thresholds (0.2 mg kg−1), possibly because of the alkaline soil pH (8.60–7.74), organic matter (7.4–65.9 g kg−1) bound to metals, and translocation of less metal to the edible plant parts by biochemical modulation. MSC can enhance subsoil fertility and promote plant development, especially in the 30% treatment. The mobility and bioavailability of heavy metals suggest that Cd is the element needing to be monitored during MSC application. High organic matter content and alkaline pH are the most important factors for controlling Cd levels. More work is required to determine the long-term impacts of sludge amendment on the soil and environment.

The effects of Cd on the bioaccumulation of P in soil-plant system have aroused wide interest and been widely explored. Sierozem has been contaminated by Cd in many areas in Northwest China. To investigate the effects of Cd on the uptake and translocation of P in plants in sierozem, pot experiments were carried out by cultivating potato (Solanum tuberosum L.) under Cd treatment. The fractions of Cd in the soil were examined by soil extraction; available P in the soil was determined; Cd and P accumulation in the plants was also determined. The result of the soil extraction shows that the acid-soluble Cd fraction gradually became the main fraction with the increasing Cd concentrations in the soil. This suggests that the change in the main fraction of Cd may promote the uptake of Cd in plants because acid-soluble Cd fraction may be utilized easily by plants. Given increasing Cd concentrations in the soil, Cd concentrations increased in each part of potato plants, whereas the soil available P and plan...

Sludge land application is now one of the most promising approaches for disposing urban sewage sludge at home and abroad Particularly in the northwest loess areas, sludge that abounds in organic matters and nutrients including N and P is applicable to improve the barren loess with loose structure Meanwhile, sludge with heavy metals is another research subject of concern. This study selected corn and wheat (two main crops in northwest of China) as test crops, and the loess added with different dry weights of composted sludge as experimental soil. The crops were planted in pots to compare the influences of different dry weights of composted sludge on the seedling growth of the crops (corn and wheat) and the absorption of heavy metals (Ni and Cd). The result indicated that composted sludge with dry weights ranging from 1% to 10% can promote the seedling growth of corn and wheat and 1% was optimal for the growth with increases about 14% and 3% for corn and wheat respectively. While more than 10% of dry weight can inhibit the growth and the inhibition effect kept pace with the dry weight of composted sludge At the end of the experiment, majority of the Ni and Cd were still accumulated in the matrix and the absorption coefficients of Ni and Cd in crops were about 0.02-0.17 and 0.02-0.12 respectively. Comparing with the control experiment, sludge land application can improve the performance of the loess and provide Ni and Cd for corn and wheat When 5% and 10% of composted sludge was added, the content of Ni and Cd contained in the experimental soil met the secondary standard (pH>7.5, Ni≤60 mg/kg and Cd ≤0.6 mg/kg) set by the Environmental Quality Standard for Soils (GB15618-1995). Therefore, to apply sludge in land use, the annual addition amount of sludge needs to satisfy both the Disposal of Sludge from Municipal Wastewater Treatment Plant-Control Standards for Agricultural Use and the Environmental Quality Standard for Soils .

With various disadvantages of pollution control technologies for toxic metal-contaminated soil, we mixed contaminated soil with sludge for in situ composting to stabilize toxic metals, so plants are enriched to take up the toxic metals. When simulating the above, we added toxic metal solution into sewage sludge, and then composed it with steel slag to determine inhibition of the availability of toxic metals. When toxic metals were added into sludge, the potential ecological index and geoaccumulation index of Cd became high while Zn was low. Steel slag had an inhibited availability of Cd, and when the adjunction of steel slag was 7%, the availability of Cd was lowest. Steel slag promoted the availability of Zn, and when the adjunction of steel slag was 27%, the availability of Zn was highest. Results showed that during composting, with increasing steel slag, Cd stabilizing time was reached sooner but Zn stabilizing time was slower, and the availability of all metals became lower. In the end, composting inhibited the potential ecological index of Cd, but it promoted the potential ecological index of Zn. Steel slag promoted the stability of Cd and Zn as Fe/Mn oxide-bound and residual species. Therefore, composting sludge and steel slag could be used as an effective inhibitor of Zn and Cd pollution.

In this study, we have a research of the development and application of agricultural composting reactor experimental apparatus. In agriculture, conversion of straw, sludge and other junk to agricultural fertilizer have a broad market prospect, it not only benefit solid waste recycling but also increase food production and food quality. Currently, the existing composting reactor had several shortcomings in practical application process, such as uneven mixing, long composting reaction cycle, producing odor and low maturity. Considering of materials and spatial structure, ventilation system, stirring system, we designed and developed a new experimental device aerobic composting reactor with relatively simple structure. We used the material in experimental device to doing a series of experiments, it include stir even, temperature changes, moisture changes, changes of organic matter, ammonia nitrogen change, change of nitrate nitrogen, PH values and so on. Experimental results showed that standard organic fertilizer could be produced by the device. Moreover, it had more complete degradation of organic matter to improve the quality of the compost product. Experiments also showed that compared with other existing devices, using the device could ferment evenly, increase the speed of biochemical reactions and reduce the fermentation time.

Municipal sludge compost (MSC) is commonly used as fertilizer or an amendment in barren soils. However, MSC-borne Cd is of great concern in food safety because of its toxicity. Loess subsoil (LS) is barren and lacks nutrients, but it has a strong ability to absorb and stabilize heavy metals. Hence, LS may be amended with MSC and may reduce the bioavailability of Cd. To simulate the dose effect of the accumulated MSC-borne Cd in amended LS, pot experiments were conducted to study the bioavailability of Cd and other mineral nutrition elements in broad bean (Vicia faba L.) under Cd stress. Plant height and dry biomass remarkably increased as the physicochemical properties of LS were significantly improved; however, they were not significantly influenced by the added Cd. The Cd in the plants grown in MSC amended-LS (P2) mainly accumulated in roots (32.12 mg kg-1) and then in stems and leaves (6.00 mg kg-1). Less Cd (0.74 mg kg-1) accumulated in the edible parts, where the Cd concentration was 53% lower than that in the edible parts of plants grown in LS (P1). The decreased Cd concentrations in the P2 beans may be due to the biomass dilution effect. Notably, the Cd concentrations in the beans exceeded the national safety limit value (0.2 mg kg-1) when the Cd treatment levels exceeded 2 mg kg-1 in LS and 6 mg kg-1 in amended LS. The MgCl2 extraction procedures can be used to assess Cd bioavailability in amended soil-plant systems. The potential antagonism of Zn and Cu against Cd toxicity in the soil-plant system may explain why this plant can tolerate higher Cd concentrations after MSC application.

Sewage sludge and industrial steel slag (SS) pose threats of serious pollution to the environment. The experiments aimed to improve the stabilizing effects of heavy metal Ni and Cd morphology in composting sludge. The total Ni and Cd species distribution and chemical forms in the compost sewage sludge were investigated with the use of compost and co-compost with SS, including degradation. The carbon/nitrogen ratio of piles was regulated with the use of sawdust prior to batch aerobic composting experiments. Results indicated that the co-composting with SS and organic matter humification can contribute to the formation of Fe and Mn hydroxides and that the humus colloid significantly changed Ni and Cd species distribution. The decreased content of Ni and Cd in an unstable state inhibited their biological activity. Conclusions were drawn that an SS amount equal to 7% of the dry sludge mass was optimal value to guarantee the lowest amount of Cd in an unstable state, whereas the amount was 14% for Ni.