Changes of Cu, Zn, and Ni chemical speciation in sewage sludge co-composted with sodium sulfide and lime

A batch composting study was performed to evaluate the feasibility of co-composting sewage sludge with sodium sulfide and lime （SSL） mixture （Na2S/CaO= 1：1）, aiming at reducing the availability of heavy metals in the sludge compost. Sewage sludge with sawdust as a bulking agent was amended with SSL at 3% （w/w, dw）, and composted for 15 d in laboratory batch reactors. The four stages of the Tessier sequential extraction method was employed to investigate changes in heavy metal fractions of Cu, Zn, and Ni in sewage sludge composted with SSL. For all the three metals, the mobile fractions, such as, exchangeable and carbonate bound were mainly transformed into low availability fractions （organic matter and sulfide, Fe-Mn oxides bound and residual forms）, and the addition of SSL enhanced this transformation. Therefore, SSL is a suitable material to co-compost with sewage sludge to reduce the availability of heavy metals. According to the cabbage seed germination test, a SSL amendment of ≤3% （w/w, dw） is recommended to co-compost with sewage sludge.

Biochar-based organic fertilizer application rates for Tetrastigma hemsleyanum planted under Moso bamboo

The under-forest economy has received increased attention in China.However,little is known about the effects of co-composted biochar on soil and plant biomass in under-forest planting systems.In this study,plant biomass,soil nutrient levels,and bacterial communities were evaluated after application of biochar-based organic fertilizer(BOF,derived from co-composted biochar-compost)at varying rates to soils supporting Tetrastigma hemsleyanum Diels&Gilg planted under a Moso bamboo(Phyllostachys edulis)forest.BOF treatment increased the biomass of T.hemsleyanum.Compared with the control,BOF application significantly increased soil pH and organic carbon(SOC).The high-throughput sequencing results showed significant differences in the Bacteroidetes,Verrucomicrobia,Chlorofexi,and OD1 phyla among all groups.At the genus level,the control group was characterized by a preponderance of Conexibacter.Rhodanobacter was enriched in soils with a 3%BOF application and Steroidobacter and Spirochaeta were the most prominent phyla in the 5%BOF group.There was no biomarker selected in the 1%BOF group at the genus level.In conclusion,BOF application increased the biomass of T.hemsleyanum when intercropped under a Moso bamboo forest;this effect may be due to changes in the soil physicochemical properties and microbial communities after BOF application.

Water extractable plant nutrients in soils amended with cow manure co-composted with maple tree residues

Studies on the availability of plant nutrients in soils treated with manure co-composted feed-stocks are very rare.The present investigation aimed at studying the nutrient release pattern from three soils amended with maple tree leaves co-composted with cow manure.Soils were mixed with the compost at the rate of 20 t/hm^(2) and incubated at room temperature.Prior to incubation,plants residue samples were analyzed for total elemental concentrations(NO_(3),NH_(4),P,K,Ca,Mg,Na,Zn,Mn,Fe,Cu,Ni and Cd).Water extractability of nutrients from soils was affected by the type of soil and ratio of composted manure applied.Extractable NH_(4),P,K,Ca and Mg concentrations varied in the descending order of sandy clay,sandy loam and silt loam except NO_(3).The concentrations of P,K,Ca and Mg in the amended soils increased with the ratio of manure co-composted with leaf litter while those of NO_(3),NH_(4) and trace elements decreased.The residual nutrients in soil varied directly with their contents in the compost amendments.Co-composting improved the availability of nutrients in soils and this should be an ideal approach to managing the enormous waste generated from the livestock sector for restoring soil fertility.

Effects of compost particle size,moisture content and binding agents on co-compost pellet properties

Composting is one of the sustainable answers for the management of organic municipal waste.Bulky nature of loose compost is one of the main drawbacks in promoting compost in agriculture and pelletization of compost can offset these drawbacks.In this study,the optimum conditions in a die and roller pelletizer to form pellets with desirable properties;bulk density,compressive strength,pellet length and disintegration ability with compost particles of different mesh sizes(2.5,3.5,5 mm),moisture contents(25%,30%,35%,40%,45%),different amounts and types of binding agents(1%,2%,3%by weight of Rice Flour(RF),Lime,Rock Phosphate(RP))were investigated.Pelletizing increased the bulk density of compost.Compost with≤5 mm particles and 25%moisture content resulted pellets with the highest compressive strength and a higher percentage of long pellets.However,the tested properties varied with the type and the amount binding agents used with compost.Disintegration was not observed in pellets free of binding agents during the tested period but binding agents enhanced disintegration.Both machine efficiency and production efficiency decreased with increased moisture in compost and increased with increased compost particle size.However,increased amounts of binding agents in compost reduced the machine efficiency.This work shows that compost pelletizing with and without binding agents,enhanced properties of compost required in transportation,storage and application in agriculture.

Dissolved organic carbon,a critical factor to increase the bioavailability of phosphorus during biochar-amended aerobic composting

Considerable research efforts have been devoted to increase phosphorus(P)availability during aerobic composting.However,there is little discussion weather the dissolved organic carbon(DOC)controls the transformation among P-fractions.Thus,we investigated the changes in DOC compositions and P-fractions during biochar-amended composting(wet weight basis,5%and 10%).TP content continuously increased since the'concentration effect'during aerobic composting.NaHCO_(3)-Pi,NaOH-Pi and HCl-Pi were main P-fractions,and biochar can improve P-bioavailability by transforming NaOH-Pi and HCl-Pi into NaHCO_(3)-Pi.Structure equation models(SEMs)indicated that biochar enhanced the P-bioavailability through regulating the decomposition of DOC.Our results at least hint that the activation mechanism on P under the influence of DOC during biochar-amended composting.

Role of rural solid waste management in non-point source pollution control of Dianchi Lake catchments, China

In recent years,with control of the main muni-cipal and industrial point pollution sources and imple-mentation of cleaning for some inner pollution sources in the water body,the discharge of point source pollution decreased gradually,while non-point source pollution has become increasingly distressing in Dianchi Lake catch-ments.As one of the major targets in non-point source pollution control,an integrated solid waste controlling strategy combined with a technological solution and man-agement system was proposed and implemented based on the waste disposal situation and characteristics of rural solid waste in the demonstration area.As the key techno-logy in rural solid waste treatment,both centralized plant-scale composting and a dispersed farmer-operated waste treating system showed promise in rendering timely ben-efits in efficiency,large handling capacity,high quality of the end product,as well as good economic return.Problems encountered during multi-substrates co-com-posting such as pathogens,high moisture content,asyn-chronism in the decomposition of different substrates,and low quality of the end product can all be tackled.92.5% of solid waste was collected in the demonstration area,while the treating and recycling ratio reached 87.9%,which pre-vented 32.2 t nitrogen and 3.9 t phosphorus per year from entering the water body of Dianchi Lake after imple-mentation of the project.